#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

long long nrZero;

long long verif(long long val)
{
    long long aux=5, Sol=0;
    while(val/aux)
    {
        Sol+=val/aux;
        aux*=5;
    }
    return Sol;
}

int main()
{
    fin>>nrZero;
    long long st=0, dr=4000000000000000000, Sol=-1;
    while(st<=dr)
    {
        long long mid=st+(dr-st)/2;
        long long rez=verif(mid);
        if(rez>=nrZero)
        {
            dr=mid-1;
            if(rez==nrZero)
                Sol=mid;
        }
        else
            st=mid+1;
    }
    fout<<Sol;
}