#include <bits/stdc++.h>
using namespace std;

int main() {
  int N, M;
  cin >> N >> M;
  
  vector<int> A(M);
  for (int i =0; i < M; i++) {
    cin >> A.at(i);
  }
  int B;
  B = 0;
 for (int i =0; i < M; i++) { 
    B += A[i];
                              }
  
  cout << N-B << endl;
  
  if ( N-B >= 0 ) {
    cout << N-B << endl;
  }
else 
  cout << -1 << endl;
}
