#include<iostream>
#include<cstdio>
#include<vector>
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];
		if (pos <= A[i])
		{
			pos--;
		}
	}
	cout << pos << endl;
	
	return 0;
}