#include <bits/stdc++.h>
using namespace std;
const long long N = 3e6;
long long n, m;
long long a[N];
long long read(void) {
  long long s = 0, w = 0;
  char c = getchar();
  while (c < '0' || c > '9') w |= c == '-', c = getchar();
  while (c >= '0' && c <= '9') s = s * 10 + c - 48, c = getchar();
  return w ? -s : s;
}
long long point(long long x) {
  if (x % 2 == 1) return x * (x - 1) / 2 + 1;
  if (x % 2 == 0) return x * (x - 1) / 2 + x / 2;
}
signed main(void) {
  n = read(), m = read();
  for (long long i = 1; i <= m; ++i) {
    long long q = read();
    a[i] = read();
  }
  sort(a + 1, a + m + 1);
  reverse(a + 1, a + m + 1);
  long long sum = 0;
  for (long long i = 1; i <= m; ++i) {
    if (point(i) > n) return cout << sum, 0;
    sum += a[i];
  }
  cout << sum << endl;
  return 0;
}
