#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int N, M, A[101010];

int main() {
  cin >> N >> M;
  for (int i = 0; i < M; i++) cin >> A[i];
  int pos = 1;
  for (int i = M - 1; i >= 0; i--) {
    if (pos == 1) pos = A[i];
    else {
      if (A[i] >= pos) pos--;
    }
  }
  cout << pos << endl;
  return 0;
}