#include <iostream>
using namespace std;

int main(){
   int n,m;
   cin >> n >> m;
   int a[m];
   for(int i = 0;i < m;i++) cin >> a[i];
   int top = 1;
   for(int i = m - 1;i >= 0;i--){
      if(top == 1) top = a[i];
      else if(top <= a[i]) top--;
   }
   cout << top << endl;
}