#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int64_t numarFactori(int64_t p,int64_t n)
{
    int64_t sol=0;
    do
    {
        sol+=n/p;
        n/=p;
    }
    while(n>0);
    return sol;
}
int64_t p,lo=0LL,hi=10000000000LL,mi;
int main()
{
    f>>p;
    while(hi-lo>1LL)
    {
        mi=(lo+hi)/2;
        if(numarFactori(5LL,mi)<p)
            lo=mi;
        else
            hi=mi;
    }
    if(numarFactori(5LL,hi)!=p)
        hi=-1;
    g<<hi;
    return 0;
}