// yukicoder: No.123 カードシャッフル
// 2019.5.13 bal4u

#include <stdio.h>

#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif
int in()
{
	int n = 0, c = gc();
	do n = 10*n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

int A[100002];
int main()
{
	int i, N, M, id;

	N = in(), M = in();
	if (N == 1) { puts("1"); return 0; }
	i = M; while (i--) A[i] = in();
	id= 1; for (i = 0; i < M; i++) {
		if (id == 1) id = A[i];
		else if (A[i] >= id) id--;
	}
	printf("%d\n", id);
	return 0;
}