#include <bits/stdc++.h>
using namespace std;
template <typename T0, typename T1>
std::ostream& operator<<(std::ostream& os, const map<T0, T1>& v) {
  for (typename map<T0, T1>::const_iterator p = v.begin(); p != v.end(); p++) {
    os << p->first << ": " << p->second << " ";
  }
  return os;
}
template <typename T0, typename T1>
std::ostream& operator<<(std::ostream& os, const pair<T0, T1>& v) {
  os << v.first << ": " << v.second << " ";
  return os;
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const vector<vector<T> >& v) {
  for (int i = 0; i < (int)v.size(); i++) {
    os << v[i] << endl;
  }
  return os;
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const vector<T>& v) {
  for (int i = 0; i < (int)v.size(); i++) {
    os << v[i] << " ";
  }
  return os;
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const set<T>& v) {
  vector<T> tmp(v.begin(), v.end());
  os << tmp;
  return os;
}
template <typename T>
std::ostream& operator<<(std::ostream& os, const deque<T>& v) {
  vector<T> tmp(v.begin(), v.end());
  os << tmp;
  return os;
}
int main() {
  long long N, M;
  while (cin >> N >> M) {
    long long lo = 1, hi = M + 1;
    while (lo + 1 < hi) {
      long long mid = (lo + hi) / 2;
      long long edges = mid * (mid - 1) / 2;
      if (mid % 2 == 0 && mid - 2 > 0) edges += (mid - 2) / 2;
      if (edges <= N - 1)
        lo = mid;
      else
        hi = mid;
    }
    vector<long long> w(M);
    for (int i = 0, _n = (M); (i) < (int)_n; ++i) {
      long long v;
      cin >> v >> w[i];
    }
    sort((w).rbegin(), (w).rend());
    cout << accumulate(&w[0], &w[lo], 0) << endl;
  }
  return 0;
}
