#include <bits/stdc++.h>
using namespace std;
long long a, b, n, m, cnt, rem, el3n2ood, mini, maxi;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> m;
  for (long long i = 1; i <= n; i++) cnt += (m + i % 5) / 5;
  cout << cnt << endl;
  cin >> n;
  return 0;
}
