#include <iostream>
#include <fstream>
using namespace std;
long long p,nr=0,n;
int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>p;
    n=0;
    if (p==0) {g<<1;return 0;}
    if (p<0)  {g<<-1;return 0;}
    else
    while (nr<=p)
    {
       if (n%25==0) nr=nr+2;
       else nr++;
       n=n+5;
    }
   g<<n;
    return 0;
}