#include <bits/stdc++.h>
using namespace std;
 
int main()
{
	int N, M;
	cin >> N >> M;
	vector<int> a( N );
	for( int i = 0; i < N; i++ ) a[i] = N - i;
	for( int i = 0; i < M; i++ ) {
		int A;
		cin >> A;
		int idx = N - A;
		int n = a[idx];
		a.erase( a.begin() + idx );
		a.push_back( n );
	}
	int ans = a[N - 1];

	cout << ans << endl;
}