#include <fstream>

using namespace std;

ifstream f("factorial.in");
ofstream g("factorial.out");

class acumulare{
public:
    int p[26];
    acumulare(){
        for(int i = 0; i <= 25; i++) p[i] = 0;
    }

    int next(){
        int i = 0, r = 1;
        p[i]++;
        while(p[i] % 5 == 0 && p[i] != 0){
            r++;
            p[i+1]++;
            p[i++] = 0;
        }
        return r;
    }
};

int main()
{
    long n, i, p = 0, ct, s = 0;
    acumulare hektori;
    f >> n;
    while(p < n){
        p += hektori.next();
        s += 5;
    }

    if(p == n) g << s;
    else g << -1;
}