#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<cstdio>
#include<stack>
using namespace std;
int main(){
    vector<int> s;
    int N,M,num;
    cin >> N >> M;
    for(int i=N;i>=1;i--)   s.push_back(i);
    while(M--){
        cin >> num;
        s.push_back(s[N-num]);
        s.erase(s.end()-num);
    }
    cout << s[N-1];
    return 0;
}