#include <bits/stdc++.h>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");
unsigned long long n,i,best,ok,st,dr,mij;
int verif(long long val)
{
    long long cnt=0,p=5;
    while(val/p>0)
    {
        cnt=cnt+val/p;
        p=p*5;
    }
    if(cnt>=n)
        return 1;
    return 0;
}
int main()
{
    fin>>n;
    st=1;
    dr=LLONG_MAX * 2-1;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        ok=verif(mij);
        if(ok==1)
        {
            best=mij;
            dr=mij-1;
        }
        else
            st=mij+1;
    }
    if(best>0)
        fout<<best;
    else
        fout<<-1;
    return 0;
}