#include <bits/stdc++.h>
using namespace std;
 
int main() {
  int N, M;
  int floor = 0;
  int step2 = -1;
  int i, j = 0;
  bool out = false;
  int pattern = 0;
  int skip = -1;
  cin >> N >> M; 
  vector<int> vec(M);
  for (i = 0; i < M; i++) {
    cin >> vec.at(i);
  }
  /////////////////////
  for(i = -1;i < N;i++){
    for(j = 1;j < N;j++){
      if((i == skip) || (i == step2)){
        j++
      }
      for(int k = 0;k < N;k++){
        while(k < M){
          if(i == vec.at(k)){
            out = true;
            break;
          }
        }
        if(out){
          break;
        }
      }
      if(out != true){
        pattern++;
      }
      step2++;
    }
    skip++;
  }
}