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

int main()
{
int i;
int iPos;
int N;
int M;
int A[ 100100 ];

	cin >> N;
	cin >> M;
	for( i = 0; i < M; i++ ) cin >> A[ i ];

	iPos = 1;
	for( i = M - 1; i >= 0; i-- )
	{
		if( iPos == 1 )
			iPos = A[ i ];
		else if( iPos <= A[ i ] )
			iPos--;
	}

	cout << iPos << endl;

	return 0;
}