#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int cinci(long long x)
{
    long long y,nr,NR;
    nr=5;
    NR=0;
    while(nr<=x)
    {
        y=x;
        NR=NR+y/nr;
        nr=nr*5;
    }
    return NR;
}
int main()
{
    int nr,p,t,ok;
    long long n,i,j,m;
    fin>>n;
    i=1;
    j=10000000000;
    ok=0;
    while(i<=j && ok==0)
    {
        m=(i+j)/2;
        t=cinci(m);
        if(t==n) {ok=1; fout<<m-m%5; }
        else if(t>n) j=m-1;
        else i=m+1;
    }
    if(ok==0) fout<<-1;
    return 0;
}