#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<ll>> vvll;
const ll inf = 1e16;
const ll md = 1000000007;

int main() {
  int n,m;
  cin>>n>>m;
  vi c(n);
  rep(i,n) c[n-1-i]=i+1;
  rep(i,m){
    int a;
    cin>>a;
    c.push_back(c[n-a]);
    c.erase(c.begin()+n-a);
  }
  cout<<c.back()<<endl;
  return 0;
}