#include <bits/stdc++.h>
using namespace std;
int main(int argc, char* argv[]) {
  ios_base::sync_with_stdio(false);
  long long int N, M;
  cin >> N >> M;
  long long int max_n1;
  for (max_n1 = 1; (max_n1 * (max_n1 - 1)) / 2 + 1 <= N; max_n1 += 2)
    ;
  max_n1 -= 2;
  long long int max_n2;
  for (max_n2 = 0; (max_n2 * (max_n2 - 1)) / 2 + max_n2 / 2 <= N; max_n2 += 2)
    ;
  max_n2 -= 2;
  long long int max_n = max(max_n1, max_n2);
  vector<long long int> qs(M, 0);
  vector<long long int> ws(M, 0);
  for (int m = 0; m < M; ++m) cin >> qs[m] >> ws[m];
  sort(ws.begin(), ws.end(), greater<long long int>());
  max_n = min(max_n, (long long int)ws.size());
  long long int res = 0;
  for (int i = 0; i < max_n; ++i) res += ws[i];
  cout << res << endl;
  return 0;
}
