The only difference between easy and hard versions is constraints.

Ivan plays a computer game that contains some microtransactions to make characters look cooler. Since Ivan wants his character to be really cool, he wants to use some of these microtransactions — and he won't start playing until he gets all of them.

Each day (during the morning) Ivan earns exactly one burle.

There are n types of microtransactions in the game. Each microtransaction costs 2 burles usually and 1 burle if it is on sale. Ivan has to order exactly k_i microtransactions of the i-th type (he orders microtransactions during the evening).

Ivan can order any (possibly zero) number of microtransactions of any types during any day (of course, if he has enough money to do it). If the microtransaction he wants to order is on sale then he can buy it for 1 burle and otherwise he can buy it for 2 burles.

There are also m special offers in the game shop. The j-th offer (d_j, t_j) means that microtransactions of the t_j-th type are on sale during the d_j-th day.

Ivan wants to order all microtransactions as soon as possible. Your task is to calculate the minimum day when he can buy all microtransactions he want and actually start playing.

Input

The first line of the input contains two integers n and m (1 ≤ n, m ≤ 1000) — the number of types of microtransactions and the number of special offers in the game shop.

The second line of the input contains n integers k_1, k_2, ..., k_n (0 ≤ k_i ≤ 1000), where k_i is the number of copies of microtransaction of the i-th type Ivan has to order. It is guaranteed that sum of all k_i is not less than 1 and not greater than 1000.

The next m lines contain special offers. The j-th of these lines contains the j-th special offer. It is given as a pair of integers (d_j, t_j) (1 ≤ d_j ≤ 1000, 1 ≤ t_j ≤ n) and means that microtransactions of the t_j-th type are on sale during the d_j-th day.

Output

Print one integer — the minimum day when Ivan can order all microtransactions he wants and actually start playing.

Examples

Input


5 6
1 2 0 2 0
2 4
3 3
1 5
1 2
1 5
2 3


Output


8


Input


5 3
4 2 1 3 2
3 5
4 2
2 5


Output


20
import java.io.*;
import java.math.BigInteger;
import java.util.*;
 
public class test {
	public static void main(String[] args) throws IOException {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		PrintWriter out = new PrintWriter(outputStream);
		InputReader in = new InputReader(inputStream);
		
//		for(int i=4;i<=4;i++) {
//			InputStream uinputStream = new FileInputStream("leftout.in");
//			String f = i+".in";
//			InputStream uinputStream = new FileInputStream(f);
//			InputReader in = new InputReader(uinputStream);
//			PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("leftout.out")));
			Task t = new Task();
			t.solve(in, out);
			out.close();			
//		}
	}	
	
	static class Task {
 
		public void solve(InputReader in, PrintWriter out) throws IOException {
//			Dumper.print(Long.MAX_VALUE);
//			int n = in.nextInt();
//			long a[] = new long[n];
//			for(int i=0;i<n;i++) {
//				a[i] = in.nextLong();
//			}
//			pair c[] = new pair[n];
//			for(int i=0;i<n;i++) {
//				a[i] *= (i+1)*(n-i);				
//				c[i] = new pair(-1*a[i],i);
//			}
//			Arrays.sort(c);
//			
//			long b[] = new long[n];
//			long d[] = new long[n];
//			for(int i=0;i<n;i++) {
//				d[i] = in.nextLong();
//			}			
//			ArrayUtils.sort(d);			
//			for(int i=0;i<n;i++) {
//				b[c[i].idx] = d[i];
//			}
//			long f = 998244353;
//			long ret[] = new long[n];
//			for(int i=n-1;i>=0;i--) {
//				ret[i]=a[i];
//				ret[i]%=f;
//				ret[i]*=b[i];
//				ret[i]%=f;
//			}
//			long v = 0;
//			for(long tmp:ret) {
//				v+=tmp;
//				v%=f;
//			}
//			out.println(v);
			int n = in.nextInt();
			int m = in.nextInt();
			int s = 0;
			int sz = 200001;
			int need[] = new int[n+1];
			for(int i=1;i<=n;i++) {
				need[i] = in.nextInt();
				s+=need[i];
			}
			Set<Integer>[] g = new HashSet[sz];
			for(int i=1;i<sz;i++) g[i] = new HashSet<Integer>();
			for(int i=0;i<m;i++) {
				int d = in.nextInt();
				int t = in.nextInt();
				g[d].add(t);
			}
			
			int l = 1;
			int r = 2*sz;
			while(l<r-1) {
				int mid = l+(r-l)/2;
				if(is_ok(g,mid,need,s)) {
					r=mid;
				}else {
					l=mid;
				}
			}
			if(is_ok(g,l,need,s)) out.println(l);
			else out.println(r);
		}
		boolean is_ok(Set<Integer>[] g, int mid, int need[], int all) {
			int offer[] = new int[need.length];
			for(int i=1;i<=Math.min(mid, g.length-1);i++) {
				for(int j:g[i]) offer[j] = i;
			}
			ArrayList<offer> arr = new ArrayList<offer>();
			for(int i=1;i<offer.length;i++) {
				if(offer[i]!=0) arr.add(new offer(i,offer[i]));
			}
			Collections.sort(arr);
			int temp[] = need.clone();
			if(arr.size()==0) return mid>=2*all;
			int cur = 0; int p=0;
			for(int i=1;i<=mid;i++) {
				cur++;
				while(p<arr.size()&&i==arr.get(p).day) {
					int item = arr.get(p).item;
					int num = temp[item];
					if(cur>=num) {
						cur-=num;
						all-=num;
						temp[item]=0;
					}else if(cur<num) {						
						temp[item]-=cur;
						all-=cur;
						cur=0;
					}
					p++;
				}
			}
			return cur>=2*all;
		}
		class offer implements Comparable<offer>{
			int item; int day;
			public offer(int a, int b) {
				item = a; day=b;
			}
			@Override
			public int compareTo(offer t) {				
				return this.day-t.day;
			}			
		}
		class pair implements Comparable<pair>{
			Long val; int idx;
			public pair(long a, int b) {
				val=a;idx=b;
			}
			@Override
			public int compareTo(pair t) {				
				return this.val.compareTo(t.val);
			}			
		}
		boolean is_prime(int a) {
			if(a==2||a==3) return true;
			for(int i=2;i<=Math.sqrt(a);i++) {
				if(a%i==0) return false;
			}
			return true;
		}
	    
		class TreeNode {
			int val;
			TreeNode left;
			TreeNode right;
			TreeNode(int x) { val = x; }
		}
	
		public int GCD(int a, int b) {
		   if (b==0) return a;
		   return GCD(b,a%b);
		}
	}
	
	
    static class ArrayUtils {
        static final long seed = System.nanoTime();
        static final Random rand = new Random(seed);
 
        public static void sort(int[] a) {
            shuffle(a);
            Arrays.sort(a);
        }
 
        public static void shuffle(int[] a) {
            for (int i = 0; i < a.length; i++) {
                int j = rand.nextInt(i + 1);
                int t = a[i];
                a[i] = a[j];
                a[j] = t;
            }
        }
        
        public static void sort(long[] a) {
            shuffle(a);
            Arrays.sort(a);
        }
 
        public static void shuffle(long[] a) {
            for (int i = 0; i < a.length; i++) {
                int j = rand.nextInt(i + 1);
                long t = a[i];
                a[i] = a[j];
                a[j] = t;
            }
        }        
 
    }	
	static class BIT{
		int arr[];
		int n;
		public BIT(int a) {
			n=a;
			arr = new int[n];
		}
		int sum(int p) {
			int s=0;
			while(p>0) {
				s+=arr[p];
				p-=p&(-p);
			}
			return s;
		}
		void add(int p, int v) {
			while(p<n) {
				arr[p]+=v;
				p+=p&(-p);
			}
		}
	}
	static class DSU{
		int[] arr;
		int[] sz;
		public DSU(int n) {
			arr = new int[n];
			sz = new int[n];
			for(int i=0;i<n;i++) arr[i] = i;
			Arrays.fill(sz, 1);
		}
		public int find(int a) {
			if(arr[a]!=a) arr[a] = find(arr[a]);
			return arr[a];
		}
		public void union(int a, int b) {
			int x = find(a);
			int y = find(b);
			if(x==y) return;
			arr[x] = y;
			sz[y] += sz[x];
		}
		public int size(int x) {
			return sz[find(x)];
		}
	}	
	static class MinHeap<Key> implements Iterable<Key> {
		private int maxN;
		private int n;
		private int[] pq;
		private int[] qp;
		private Key[] keys;
		private Comparator<Key> comparator;
		
		public MinHeap(int capacity){
			if (capacity < 0) throw new IllegalArgumentException();
			this.maxN = capacity;
			n=0;
			pq = new int[maxN+1];
			qp = new int[maxN+1];
			keys = (Key[]) new Object[capacity+1];
			Arrays.fill(qp, -1);
		}
		
		public MinHeap(int capacity, Comparator<Key> c){
			if (capacity < 0) throw new IllegalArgumentException();
			this.maxN = capacity;
			n=0;
			pq = new int[maxN+1];
			qp = new int[maxN+1];
			keys = (Key[]) new Object[capacity+1];
			Arrays.fill(qp, -1);
			comparator = c;
		}			
		public boolean isEmpty()	{ return n==0; 	}
		public int size()			{ return n;		}
		public boolean contains(int i) {
	        if (i < 0 || i >= maxN) throw new IllegalArgumentException();
	        return qp[i] != -1;
		}	
		public int peekIdx() {
	        if (n == 0) throw new NoSuchElementException("Priority queue underflow");
	        return pq[1];		
		}	
		public Key peek(){
			if(isEmpty()) throw new NoSuchElementException("Priority queue underflow");
			return keys[pq[1]];
		}
		public int poll(){
			if(isEmpty()) throw new NoSuchElementException("Priority queue underflow");
			int min = pq[1];
			exch(1,n--);
			down(1);
			assert min==pq[n+1];
			qp[min] = -1;
			keys[min] = null;		
			pq[n+1] = -1;
			return min;
		}
	    public void update(int i, Key key) {
	        if (i < 0 || i >= maxN) throw new IllegalArgumentException();
	        if (!contains(i)) {
	        	this.add(i, key);
	        }else {
	        	keys[i] = key;
	        	up(qp[i]);
	        	down(qp[i]);
	        }
	    }	
		private void add(int i, Key x){
	        if (i < 0 || i >= maxN) throw new IllegalArgumentException();
	        if (contains(i)) throw new IllegalArgumentException("index is already in the priority queue");
	        n++;
	        qp[i] = n;
	        pq[n] = i;
	        keys[i] = x;
	        up(n);
		}
		private void up(int k){
			while(k>1&&less(k,k/2)){
				exch(k,k/2);
				k/=2;
			}
		}
		private void down(int k){
			while(2*k<=n){
				int j=2*k;
				if(j<n&&less(j+1,j)) j++;
				if(less(k,j)) break;
				exch(k,j);
				k=j;
			}
		}
		
		public boolean less(int i, int j){
	        if (comparator == null) {
	            return ((Comparable<Key>) keys[pq[i]]).compareTo(keys[pq[j]]) < 0;
	        }
	        else {
	            return comparator.compare(keys[pq[i]], keys[pq[j]]) < 0;
	        }
		}
 
		public void exch(int i, int j){
	        int swap = pq[i];
	        pq[i] = pq[j];
	        pq[j] = swap;
	        qp[pq[i]] = i;
	        qp[pq[j]] = j;
		}
 
		@Override
		public Iterator<Key> iterator() {
			// TODO Auto-generated method stub
			return null;
		}
	}  	
 
    private static class InputReader
    {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int zcurChar;
        private int znumChars;
        private SpaceCharFilter filter;
 
        public InputReader(InputStream stream)
        {
            this.stream = stream;
        }
 
        public int read()
        {
            if (znumChars == -1)
                throw new InputMismatchException();
            if (zcurChar >= znumChars)
            {
            	zcurChar = 0;
                try
                {
                    znumChars = stream.read(buf);
                } catch (IOException e)
                {
                    throw new InputMismatchException();
                }
                if (znumChars <= 0)
                    return -1;
            }
            return buf[zcurChar++];
        }
 
        public int nextInt()
        {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-')
            {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do
            {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
 
        public String nextString()
        {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do
            {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }
 
        public double nextDouble()
        {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-')
            {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.')
            {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.')
            {
                c = read();
                double m = 1;
                while (!isSpaceChar(c))
                {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }
 
        public long nextLong()
        {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-')
            {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do
            {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }
 
        public boolean isSpaceChar(int c)
        {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        public String next()
        {
            return nextString();
        }
 
        public interface SpaceCharFilter
        {
            public boolean isSpaceChar(int ch);
        }
        public int[] readIntArray(int n) {
            int[] ret = new int[n];
            for (int i = 0; i < n; i++) {
                ret[i] = nextInt();
            }
            return ret;
        }        
    }    
 
	static class Dumper {
		static void print_int_arr(int[] arr) {
			for (int i = 0; i < arr.length; i++) {
				System.out.print(arr[i] + " ");
			}
			System.out.println();
			System.out.println("---------------------");
		}
 
		static void print_char_arr(char[] arr) {
			for (int i = 0; i < arr.length; i++) {
				System.out.print(arr[i] + " ");
			}
			System.out.println();
			System.out.println("---------------------");
		}
 
		static void print_double_arr(double[] arr) {
			for (int i = 0; i < arr.length; i++) {
				System.out.print(arr[i] + " ");
			}
			System.out.println();
			System.out.println("---------------------");
		}
 
		static void print_2d_arr(int[][] arr, int x, int y) {
			for (int i = 0; i < x; i++) {
				for (int j = 0; j < y; j++) {
					System.out.print(arr[i][j] + " ");
				}
				System.out.println();
			}
			System.out.println();
			System.out.println("---------------------");
		}
 
		static void print_2d_arr(boolean[][] arr, int x, int y) {
			for (int i = 0; i < x; i++) {
				for (int j = 0; j < y; j++) {
					System.out.print(arr[i][j] + " ");
				}
				System.out.println();
			}
			System.out.println();
			System.out.println("---------------------");
		}
 
		static void print(Object o) {
			System.out.println(o.toString());
		}
 
		static void getc() {
			System.out.println("here");
		}
	}
}