#include <fstream>
using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");
int main (void)
{
    unsigned long long a,l=0,best=1;
    in>>a;
    int r=a*5;
    int copie=a;
    if (a==0)
    {
        out<<'1';
        return 0;
    }
    while (copie%5==0)
        copie/=5;
    if (copie==1)
    {
        out<<-1;
        return 0;
    }
    while (l<=r)
    {
        int mid=(l+r)/2,sol=0;
        for (int d=5;d<=mid;d*=5)
            sol+=mid/d;
        if (sol>=a)
        {
            best=mid;
            r=mid-1;
        }
        else
            l=mid+1;
    }
    out<<best;
    return 0;
}