#include <fstream>
using namespace std;
int fr[10];
int main()
{
    long long n,p,cop;
    ifstream in("fact.in");
    ofstream out("fact.out");
    in>>p;
    n=1;
    while(fr[5]<p)
    {
        cop=n;
        while(cop>1)
        {

            while(cop%5==0)
            {
                cop/=5;
                fr[5]++;
            }
            break;
        }
        n++;
    }
    if(fr[5]==p)
        out<<n-1;
    else
        out<<-1;
    return 0;
}