def main():

    X = int(eval(input()))

    ans = 1

    while ans * (ans + 1) * 0.5 < X:

        ans += 1

    print(ans)

    return





main()

from operator import rshift





def main():

    X = int(eval(input()))

    ans = 1

    while rshift(ans * (ans + 1), 1) < X:

        ans += 1

    print(ans)

    return





main()

def main():
    X = int(eval(input()))
    ans = 1
    while ans * (ans + 1) * 0.5 < X:
        ans += 1
    print(ans)
    return


main()

from operator import rshift


def main():
    X = int(eval(input()))
    ans = 1
    while rshift(ans * (ans + 1), 1) < X:
        ans += 1
    print(ans)
    return


main()

+from operator import rshift + + -    while ans * (ans + 1) * 0.5 < X: +    while rshift(ans * (ans + 1), 1) < X: