Manao is trying to open a rather challenging lock. The lock has n buttons on it and to open it, you should press the buttons in a certain order to open the lock. When you push some button, it either stays pressed into the lock (that means that you've guessed correctly and pushed the button that goes next in the sequence), or all pressed buttons return to the initial position. When all buttons are pressed into the lock at once, the lock opens.

Consider an example with three buttons. Let's say that the opening sequence is: {2, 3, 1}. If you first press buttons 1 or 3, the buttons unpress immediately. If you first press button 2, it stays pressed. If you press 1 after 2, all buttons unpress. If you press 3 after 2, buttons 3 and 2 stay pressed. As soon as you've got two pressed buttons, you only need to press button 1 to open the lock.

Manao doesn't know the opening sequence. But he is really smart and he is going to act in the optimal way. Calculate the number of times he's got to push a button in order to open the lock in the worst-case scenario.

Input

A single line contains integer n (1 ≤ n ≤ 2000) — the number of buttons the lock has.

Output

In a single line print the number of times Manao has to push a button in the worst-case scenario.

Examples

Input

2


Output

3


Input

3


Output

7

Note

Consider the first test sample. Manao can fail his first push and push the wrong button. In this case he will already be able to guess the right one with his second push. And his third push will push the second right button. Thus, in the worst-case scenario he will only need 3 pushes.
l = [2, 4, 7, 11, 16, 22, 29, 37, 46, 56, 67, 79, 92, 106, 121, 137, 154, 172, 191, 211, 232, 254, 277, 301, 326, 352, 379, 407, 436, 466, 497, 529, 562, 596, 631, 667, 704, 742, 781, 821, 862, 904, 947, 991, 1036, 1082, 1129, 1177, 1226, 1276, 1327, 1379, 1432, 1486, 1541, 1597, 1654, 1712, 1771, 1831, 1892, 1954, 2017, 2081, 2146, 2212, 2279, 2347, 2416, 2486, 2557, 2629, 2702, 2776, 2851, 2927, 3004, 3082, 3161, 3241, 3322, 3404, 3487, 3571, 3656, 3742, 3829, 3917, 4006, 4096, 4187, 4279, 4372, 4466, 4561, 4657, 4754, 4852, 4951, 5051, 5152, 5254, 5357, 5461, 5566, 5672, 5779, 5887, 5996, 6106, 6217, 6329, 6442, 6556, 6671, 6787, 6904, 7022, 7141, 7261, 7382, 7504, 7627, 7751, 7876, 8002, 8129, 8257, 8386, 8516, 8647, 8779, 8912, 9046, 9181, 9317, 9454, 9592, 9731, 9871, 10012, 10154, 10297, 10441, 10586, 10732, 10879, 11027, 11176, 11326, 11477, 11629, 11782, 11936, 12091, 12247, 12404, 12562, 12721, 12881, 13042, 13204, 13367, 13531, 13696, 13862, 14029, 14197, 14366, 14536, 14707, 14879, 15052, 15226, 15401, 15577, 15754, 15932, 16111, 16291, 16472, 16654, 16837, 17021, 17206, 17392, 17579, 17767, 17956, 18146, 18337, 18529, 18722, 18916, 19111, 19307, 19504, 19702, 19901, 20101, 20302, 20504, 20707, 20911, 21116, 21322, 21529, 21737, 21946, 22156, 22367, 22579, 22792, 23006, 23221, 23437, 23654, 23872, 24091, 24311, 24532, 24754, 24977, 25201, 25426, 25652, 25879, 26107, 26336, 26566, 26797, 27029, 27262, 27496, 27731, 27967, 28204, 28442, 28681, 28921, 29162, 29404, 29647, 29891, 30136, 30382, 30629, 30877, 31126, 31376, 31627, 31879, 32132, 32386, 32641, 32897, 33154, 33412, 33671, 33931, 34192, 34454, 34717, 34981, 35246, 35512, 35779, 36047, 36316, 36586, 36857, 37129, 37402, 37676, 37951, 38227, 38504, 38782, 39061, 39341, 39622, 39904, 40187, 40471, 40756, 41042, 41329, 41617, 41906, 42196, 42487, 42779, 43072, 43366, 43661, 43957, 44254, 44552, 44851, 45151, 45452, 45754, 46057, 46361, 46666, 46972, 47279, 47587, 47896, 48206, 48517, 48829, 49142, 49456, 49771, 50087, 50404, 50722, 51041, 51361, 51682, 52004, 52327, 52651, 52976, 53302, 53629, 53957, 54286, 54616, 54947, 55279, 55612, 55946, 56281, 56617, 56954, 57292, 57631, 57971, 58312, 58654, 58997, 59341, 59686, 60032, 60379, 60727, 61076, 61426, 61777, 62129, 62482, 62836, 63191, 63547, 63904, 64262, 64621, 64981, 65342, 65704, 66067, 66431, 66796, 67162, 67529, 67897, 68266, 68636, 69007, 69379, 69752, 70126, 70501, 70877, 71254, 71632, 72011, 72391, 72772, 73154, 73537, 73921, 74306, 74692, 75079, 75467, 75856, 76246, 76637, 77029, 77422, 77816, 78211, 78607, 79004, 79402, 79801, 80201, 80602, 81004, 81407, 81811, 82216, 82622, 83029, 83437, 83846, 84256, 84667, 85079, 85492, 85906, 86321, 86737, 87154, 87572, 87991, 88411, 88832, 89254, 89677, 90101, 90526, 90952, 91379, 91807, 92236, 92666, 93097, 93529, 93962, 94396, 94831, 95267, 95704, 96142, 96581, 97021, 97462, 97904, 98347, 98791, 99236, 99682, 100129, 100577, 101026, 101476, 101927, 102379, 102832, 103286, 103741, 104197, 104654, 105112, 105571, 106031, 106492, 106954, 107417, 107881, 108346, 108812, 109279, 109747, 110216, 110686, 111157, 111629, 112102, 112576, 113051, 113527, 114004, 114482, 114961, 115441, 115922, 116404, 116887, 117371, 117856, 118342, 118829, 119317, 119806, 120296, 120787, 121279, 121772, 122266, 122761, 123257, 123754, 124252, 124751, 125251, 125752, 126254, 126757, 127261, 127766, 128272, 128779, 129287, 129796, 130306, 130817, 131329, 131842, 132356, 132871, 133387, 133904, 134422, 134941, 135461, 135982, 136504, 137027, 137551, 138076, 138602, 139129, 139657, 140186, 140716, 141247, 141779, 142312, 142846, 143381, 143917, 144454, 144992, 145531, 146071, 146612, 147154, 147697, 148241, 148786, 149332, 149879, 150427, 150976, 151526, 152077, 152629, 153182, 153736, 154291, 154847, 155404, 155962, 156521, 157081, 157642, 158204, 158767, 159331, 159896, 160462, 161029, 161597, 162166, 162736, 163307, 163879, 164452, 165026, 165601, 166177, 166754, 167332, 167911, 168491, 169072, 169654, 170237, 170821, 171406, 171992, 172579, 173167, 173756, 174346, 174937, 175529, 176122, 176716, 177311, 177907, 178504, 179102, 179701, 180301, 180902, 181504, 182107, 182711, 183316, 183922, 184529, 185137, 185746, 186356, 186967, 187579, 188192, 188806, 189421, 190037, 190654, 191272, 191891, 192511, 193132, 193754, 194377, 195001, 195626, 196252, 196879, 197507, 198136, 198766, 199397, 200029, 200662, 201296, 201931, 202567, 203204, 203842, 204481, 205121, 205762, 206404, 207047, 207691, 208336, 208982, 209629, 210277, 210926, 211576, 212227, 212879, 213532, 214186, 214841, 215497, 216154, 216812, 217471, 218131, 218792, 219454, 220117, 220781, 221446, 222112, 222779, 223447, 224116, 224786, 225457, 226129, 226802, 227476, 228151, 228827, 229504, 230182, 230861, 231541, 232222, 232904, 233587, 234271, 234956, 235642, 236329, 237017, 237706, 238396, 239087, 239779, 240472, 241166, 241861, 242557, 243254, 243952, 244651, 245351, 246052, 246754, 247457, 248161, 248866, 249572, 250279, 250987, 251696, 252406, 253117, 253829, 254542, 255256, 255971, 256687, 257404, 258122, 258841, 259561, 260282, 261004, 261727, 262451, 263176, 263902, 264629, 265357, 266086, 266816, 267547, 268279, 269012, 269746, 270481, 271217, 271954, 272692, 273431, 274171, 274912, 275654, 276397, 277141, 277886, 278632, 279379, 280127, 280876, 281626, 282377, 283129, 283882, 284636, 285391, 286147, 286904, 287662, 288421, 289181, 289942, 290704, 291467, 292231, 292996, 293762, 294529, 295297, 296066, 296836, 297607, 298379, 299152, 299926, 300701, 301477, 302254, 303032, 303811, 304591, 305372, 306154, 306937, 307721, 308506, 309292, 310079, 310867, 311656, 312446, 313237, 314029, 314822, 315616, 316411, 317207, 318004, 318802, 319601, 320401, 321202, 322004, 322807, 323611, 324416, 325222, 326029, 326837, 327646, 328456, 329267, 330079, 330892, 331706, 332521, 333337, 334154, 334972, 335791, 336611, 337432, 338254, 339077, 339901, 340726, 341552, 342379, 343207, 344036, 344866, 345697, 346529, 347362, 348196, 349031, 349867, 350704, 351542, 352381, 353221, 354062, 354904, 355747, 356591, 357436, 358282, 359129, 359977, 360826, 361676, 362527, 363379, 364232, 365086, 365941, 366797, 367654, 368512, 369371, 370231, 371092, 371954, 372817, 373681, 374546, 375412, 376279, 377147, 378016, 378886, 379757, 380629, 381502, 382376, 383251, 384127, 385004, 385882, 386761, 387641, 388522, 389404, 390287, 391171, 392056, 392942, 393829, 394717, 395606, 396496, 397387, 398279, 399172, 400066, 400961, 401857, 402754, 403652, 404551, 405451, 406352, 407254, 408157, 409061, 409966, 410872, 411779, 412687, 413596, 414506, 415417, 416329, 417242, 418156, 419071, 419987, 420904, 421822, 422741, 423661, 424582, 425504, 426427, 427351, 428276, 429202, 430129, 431057, 431986, 432916, 433847, 434779, 435712, 436646, 437581, 438517, 439454, 440392, 441331, 442271, 443212, 444154, 445097, 446041, 446986, 447932, 448879, 449827, 450776, 451726, 452677, 453629, 454582, 455536, 456491, 457447, 458404, 459362, 460321, 461281, 462242, 463204, 464167, 465131, 466096, 467062, 468029, 468997, 469966, 470936, 471907, 472879, 473852, 474826, 475801, 476777, 477754, 478732, 479711, 480691, 481672, 482654, 483637, 484621, 485606, 486592, 487579, 488567, 489556, 490546, 491537, 492529, 493522, 494516, 495511, 496507, 497504, 498502, 499501, 500501, 501502, 502504, 503507, 504511, 505516, 506522, 507529, 508537, 509546, 510556, 511567, 512579, 513592, 514606, 515621, 516637, 517654, 518672, 519691, 520711, 521732, 522754, 523777, 524801, 525826, 526852, 527879, 528907, 529936, 530966, 531997, 533029, 534062, 535096, 536131, 537167, 538204, 539242, 540281, 541321, 542362, 543404, 544447, 545491, 546536, 547582, 548629, 549677, 550726, 551776, 552827, 553879, 554932, 555986, 557041, 558097, 559154, 560212, 561271, 562331, 563392, 564454, 565517, 566581, 567646, 568712, 569779, 570847, 571916, 572986, 574057, 575129, 576202, 577276, 578351, 579427, 580504, 581582, 582661, 583741, 584822, 585904, 586987, 588071, 589156, 590242, 591329, 592417, 593506, 594596, 595687, 596779, 597872, 598966, 600061, 601157, 602254, 603352, 604451, 605551, 606652, 607754, 608857, 609961, 611066, 612172, 613279, 614387, 615496, 616606, 617717, 618829, 619942, 621056, 622171, 623287, 624404, 625522, 626641, 627761, 628882, 630004, 631127, 632251, 633376, 634502, 635629, 636757, 637886, 639016, 640147, 641279, 642412, 643546, 644681, 645817, 646954, 648092, 649231, 650371, 651512, 652654, 653797, 654941, 656086, 657232, 658379, 659527, 660676, 661826, 662977, 664129, 665282, 666436, 667591, 668747, 669904, 671062, 672221, 673381, 674542, 675704, 676867, 678031, 679196, 680362, 681529, 682697, 683866, 685036, 686207, 687379, 688552, 689726, 690901, 692077, 693254, 694432, 695611, 696791, 697972, 699154, 700337, 701521, 702706, 703892, 705079, 706267, 707456, 708646, 709837, 711029, 712222, 713416, 714611, 715807, 717004, 718202, 719401, 720601, 721802, 723004, 724207, 725411, 726616, 727822, 729029, 730237, 731446, 732656, 733867, 735079, 736292, 737506, 738721, 739937, 741154, 742372, 743591, 744811, 746032, 747254, 748477, 749701, 750926, 752152, 753379, 754607, 755836, 757066, 758297, 759529, 760762, 761996, 763231, 764467, 765704, 766942, 768181, 769421, 770662, 771904, 773147, 774391, 775636, 776882, 778129, 779377, 780626, 781876, 783127, 784379, 785632, 786886, 788141, 789397, 790654, 791912, 793171, 794431, 795692, 796954, 798217, 799481, 800746, 802012, 803279, 804547, 805816, 807086, 808357, 809629, 810902, 812176, 813451, 814727, 816004, 817282, 818561, 819841, 821122, 822404, 823687, 824971, 826256, 827542, 828829, 830117, 831406, 832696, 833987, 835279, 836572, 837866, 839161, 840457, 841754, 843052, 844351, 845651, 846952, 848254, 849557, 850861, 852166, 853472, 854779, 856087, 857396, 858706, 860017, 861329, 862642, 863956, 865271, 866587, 867904, 869222, 870541, 871861, 873182, 874504, 875827, 877151, 878476, 879802, 881129, 882457, 883786, 885116, 886447, 887779, 889112, 890446, 891781, 893117, 894454, 895792, 897131, 898471, 899812, 901154, 902497, 903841, 905186, 906532, 907879, 909227, 910576, 911926, 913277, 914629, 915982, 917336, 918691, 920047, 921404, 922762, 924121, 925481, 926842, 928204, 929567, 930931, 932296, 933662, 935029, 936397, 937766, 939136, 940507, 941879, 943252, 944626, 946001, 947377, 948754, 950132, 951511, 952891, 954272, 955654, 957037, 958421, 959806, 961192, 962579, 963967, 965356, 966746, 968137, 969529, 970922, 972316, 973711, 975107, 976504, 977902, 979301, 980701, 982102, 983504, 984907, 986311, 987716, 989122, 990529, 991937, 993346, 994756, 996167, 997579, 998992, 1000406, 1001821, 1003237, 1004654, 1006072, 1007491, 1008911, 1010332, 1011754, 1013177, 1014601, 1016026, 1017452, 1018879, 1020307, 1021736, 1023166, 1024597, 1026029, 1027462, 1028896, 1030331, 1031767, 1033204, 1034642, 1036081, 1037521, 1038962, 1040404, 1041847, 1043291, 1044736, 1046182, 1047629, 1049077, 1050526, 1051976, 1053427, 1054879, 1056332, 1057786, 1059241, 1060697, 1062154, 1063612, 1065071, 1066531, 1067992, 1069454, 1070917, 1072381, 1073846, 1075312, 1076779, 1078247, 1079716, 1081186, 1082657, 1084129, 1085602, 1087076, 1088551, 1090027, 1091504, 1092982, 1094461, 1095941, 1097422, 1098904, 1100387, 1101871, 1103356, 1104842, 1106329, 1107817, 1109306, 1110796, 1112287, 1113779, 1115272, 1116766, 1118261, 1119757, 1121254, 1122752, 1124251, 1125751, 1127252, 1128754, 1130257, 1131761, 1133266, 1134772, 1136279, 1137787, 1139296, 1140806, 1142317, 1143829, 1145342, 1146856, 1148371, 1149887, 1151404, 1152922, 1154441, 1155961, 1157482, 1159004, 1160527, 1162051, 1163576, 1165102, 1166629, 1168157, 1169686, 1171216, 1172747, 1174279, 1175812, 1177346, 1178881, 1180417, 1181954, 1183492, 1185031, 1186571, 1188112, 1189654, 1191197, 1192741, 1194286, 1195832, 1197379, 1198927, 1200476, 1202026, 1203577, 1205129, 1206682, 1208236, 1209791, 1211347, 1212904, 1214462, 1216021, 1217581, 1219142, 1220704, 1222267, 1223831, 1225396, 1226962, 1228529, 1230097, 1231666, 1233236, 1234807, 1236379, 1237952, 1239526, 1241101, 1242677, 1244254, 1245832, 1247411, 1248991, 1250572, 1252154, 1253737, 1255321, 1256906, 1258492, 1260079, 1261667, 1263256, 1264846, 1266437, 1268029, 1269622, 1271216, 1272811, 1274407, 1276004, 1277602, 1279201, 1280801, 1282402, 1284004, 1285607, 1287211, 1288816, 1290422, 1292029, 1293637, 1295246, 1296856, 1298467, 1300079, 1301692, 1303306, 1304921, 1306537, 1308154, 1309772, 1311391, 1313011, 1314632, 1316254, 1317877, 1319501, 1321126, 1322752, 1324379, 1326007, 1327636, 1329266, 1330897, 1332529, 1334162, 1335796, 1337431, 1339067, 1340704, 1342342, 1343981, 1345621, 1347262, 1348904, 1350547, 1352191, 1353836, 1355482, 1357129, 1358777, 1360426, 1362076, 1363727, 1365379, 1367032, 1368686, 1370341, 1371997, 1373654, 1375312, 1376971, 1378631, 1380292, 1381954, 1383617, 1385281, 1386946, 1388612, 1390279, 1391947, 1393616, 1395286, 1396957, 1398629, 1400302, 1401976, 1403651, 1405327, 1407004, 1408682, 1410361, 1412041, 1413722, 1415404, 1417087, 1418771, 1420456, 1422142, 1423829, 1425517, 1427206, 1428896, 1430587, 1432279, 1433972, 1435666, 1437361, 1439057, 1440754, 1442452, 1444151, 1445851, 1447552, 1449254, 1450957, 1452661, 1454366, 1456072, 1457779, 1459487, 1461196, 1462906, 1464617, 1466329, 1468042, 1469756, 1471471, 1473187, 1474904, 1476622, 1478341, 1480061, 1481782, 1483504, 1485227, 1486951, 1488676, 1490402, 1492129, 1493857, 1495586, 1497316, 1499047, 1500779, 1502512, 1504246, 1505981, 1507717, 1509454, 1511192, 1512931, 1514671, 1516412, 1518154, 1519897, 1521641, 1523386, 1525132, 1526879, 1528627, 1530376, 1532126, 1533877, 1535629, 1537382, 1539136, 1540891, 1542647, 1544404, 1546162, 1547921, 1549681, 1551442, 1553204, 1554967, 1556731, 1558496, 1560262, 1562029, 1563797, 1565566, 1567336, 1569107, 1570879, 1572652, 1574426, 1576201, 1577977, 1579754, 1581532, 1583311, 1585091, 1586872, 1588654, 1590437, 1592221, 1594006, 1595792, 1597579, 1599367, 1601156, 1602946, 1604737, 1606529, 1608322, 1610116, 1611911, 1613707, 1615504, 1617302, 1619101, 1620901, 1622702, 1624504, 1626307, 1628111, 1629916, 1631722, 1633529, 1635337, 1637146, 1638956, 1640767, 1642579, 1644392, 1646206, 1648021, 1649837, 1651654, 1653472, 1655291, 1657111, 1658932, 1660754, 1662577, 1664401, 1666226, 1668052, 1669879, 1671707, 1673536, 1675366, 1677197, 1679029, 1680862, 1682696, 1684531, 1686367, 1688204, 1690042, 1691881, 1693721, 1695562, 1697404, 1699247, 1701091, 1702936, 1704782, 1706629, 1708477, 1710326, 1712176, 1714027, 1715879, 1717732, 1719586, 1721441, 1723297, 1725154, 1727012, 1728871, 1730731, 1732592, 1734454, 1736317, 1738181, 1740046, 1741912, 1743779, 1745647, 1747516, 1749386, 1751257, 1753129, 1755002, 1756876, 1758751, 1760627, 1762504, 1764382, 1766261, 1768141, 1770022, 1771904, 1773787, 1775671, 1777556, 1779442, 1781329, 1783217, 1785106, 1786996, 1788887, 1790779, 1792672, 1794566, 1796461, 1798357, 1800254, 1802152, 1804051, 1805951, 1807852, 1809754, 1811657, 1813561, 1815466, 1817372, 1819279, 1821187, 1823096, 1825006, 1826917, 1828829, 1830742, 1832656, 1834571, 1836487, 1838404, 1840322, 1842241, 1844161, 1846082, 1848004, 1849927, 1851851, 1853776, 1855702, 1857629, 1859557, 1861486, 1863416, 1865347, 1867279, 1869212, 1871146, 1873081, 1875017, 1876954, 1878892, 1880831, 1882771, 1884712, 1886654, 1888597, 1890541, 1892486, 1894432, 1896379, 1898327, 1900276, 1902226, 1904177, 1906129, 1908082, 1910036, 1911991, 1913947, 1915904, 1917862, 1919821, 1921781, 1923742, 1925704, 1927667, 1929631, 1931596, 1933562, 1935529, 1937497, 1939466, 1941436, 1943407, 1945379, 1947352, 1949326, 1951301, 1953277, 1955254, 1957232, 1959211, 1961191, 1963172, 1965154, 1967137, 1969121, 1971106, 1973092, 1975079, 1977067, 1979056, 1981046, 1983037, 1985029, 1987022, 1989016, 1991011, 1993007, 1995004, 1997002, 1999001, 2001001]
n = int(input())
print(1 + sum(l[:n-1]))