#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a;i < n;i++)
#define per(i,n,a) for (int i = n-1;i >= a;i--)
using namespace std;

int main() {
    int N, M; cin >> N >> M;
    vector<int> A(M);
    rep(i,0,M){
        cin >> A[i];
    }
    int pos = 1;
    per(i,M,0){
        if (pos == 1) pos = A[i];
        else if (A[i] >= pos) pos--;
    }
    cout << pos << endl;
}