#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n, m, count = 0;
  cin >> n >> m;
  for (int i = 1; i <= n; i++) count += (m + (i % 5)) / 5;
  cout << count;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
