#include <iostream>
using namespace std;
signed main() {
int n;
cin >> n;
int sum = 0;
for(int i = 5; i <= n; i += 5) sum += i;
cout << sum;
}
#include <iostream>
using namespace std;
signed main() {
int n;
cin >> n;
int sum = 0;
for(int i = 5; i <= n; i += 5) sum += i;
cout << sum;
}