#include <iostream>
#include <fstream>
using namespace std;

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

long long p;

int zero(long n)
{
    int nr=0;
    while(n>=5)
    {
        nr+=n/5;
        n/=5;
    }
    return nr;
}

void cautbin()
{
    long long i=0;
    long long pas=1<<30;
    while(pas!=0)
    {
        if(zero(i+pas)<p)
            i+=pas;
    pas/=2;
    }
    if(zero(i+1)==p){
        out<<i+1;
    }
    else
    {
        out<<-1;
    }
}

int main()
{
    in>>p;
    cautbin();
    return 0;
}