#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m;
  cin >> n >> m;
  long long ans = 0;
  for (int i = 1; i <= n; ++i) {
    long long now = i % 5;
    ans += (m + now) / 5;
  }
  cout << ans << endl;
  return 0;
}
