#include <stdio.h>

void chmin(int* a, int b)
{
	if (*a > b) *a = b;
}

int main()
{
	int i, N, M, A[1001], B[1001];
	scanf("%d %d", &N, &M);
	for (i = 1; i <= N; i++) scanf("%d", &(A[i]));
	for (i = 1; i <= M; i++) scanf("%d", &(B[i]));
	
	int j, ii, jj, a, b, dp[2][6001], cur, prev;
	for (j = 1, jj = 1, b = B[1], dp[0][0] = 0; jj <= M; j++) {
		dp[0][j] = j;
		if (b == 0) {
			jj++;
			b = B[jj];
		} else b--;
	}
	for (i = 1, ii = 1, a = A[1], cur = 1, prev = 0; ii <= N; i++, cur ^= 1, prev ^= 1) {
		if (a == 0) {
			ii++;
			a = A[ii];
			for (j = 1, jj = 1, b = B[1], dp[cur][0] = i; jj <= M; j++) {
				if (b == 0) {
					jj++;
					b = B[jj];
					dp[cur][j] = dp[prev][j-1];
				} else {
					b--;
					dp[cur][j] = dp[prev][j-1];
					chmin(&(dp[cur][j]), dp[prev][j]);
					chmin(&(dp[cur][j]), dp[cur][j-1]);
					dp[cur][j]++;
				}
			}
		} else {
			a--;
			for (j = 1, jj = 1, b = B[1], dp[cur][0] = i; jj <= M; j++) {
				if (b == 0) {
					jj++;
					b = B[jj];
					dp[cur][j] = dp[prev][j-1];
					chmin(&(dp[cur][j]), dp[prev][j]);
					chmin(&(dp[cur][j]), dp[cur][j-1]);
					dp[cur][j]++;
				} else {
					b--;
					dp[cur][j] = dp[prev][j-1];
				}
			}
		}
	}
	printf("%d\n", dp[prev][j-1]);
	fflush(stdout);
	return 0;
}