#include "bits/stdc++.h"
using namespace std;


int main() {
	int N, M;
	cin >> N >> M;
	vector<int> A(M);
	for (int i = 0; i < M; i++)
	{
		cin >> A[i];
	}

	int pos = 1;
	for (int i = M - 1; i >= 0; i--)
	{
		if (pos == 1) pos = A[i];
		else{
			if (A[i] >= pos) pos--;
		}
	}
	cout << pos << endl;
}