#include <iostream>
#include <fstream>
#include <limits.h>

using namespace std;

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

long long p,st,dr,nr_zero,ret;

long long zeros(long long n)
{
    long long nr_zero=0;
    for(long long i=5LL;i<=n;i*=5LL)
        nr_zero+=n/i;
    return nr_zero;
}

int main()
{
    fin >> p;
    st=1;
    dr=LONG_MAX;
    while(st<=dr)
    {
        long long m=st+(dr-st)/2;
        nr_zero=zeros(m);
        if(nr_zero==p)
        {
            ret=m;
            dr=m-1;
        }
        else if(p<nr_zero)
            dr=m-1;
        else
            st=m+1;
    }
    fout << (ret?ret:-1);
    return 0;
}