#include <bits/stdc++.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
unsigned long long p;
unsigned long long verif(unsigned long long limit)
{
    unsigned long long ct=0, p, i;
    for(p=5; p<=limit; p*=5)
        ct+=limit/p;
    return ct;
}
int main()
{
    unsigned long long st, dr, mijl, x;
    fin>>p;
    if(p==0)
    {
        fout<<1<<'\n';
        return 0;
    }
    st=1, dr=p*5;
    while(st<=dr)
    {
        mijl=(st+dr)>>1;
        x=verif(mijl);
        if(x==p)
        {
            while(mijl%5!=0)
                mijl--;
            fout<<mijl<<'\n';
            return 0;
        }
        if(x>p)
            dr=mijl-1;
        else
            st=mijl+1;
    }
    fout<<-1<<'\n';
    return 0;
}