#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

long long p,WK;

int nr0(long long n)
{
    long long  k=5,s=0;
    while (n/k)
    {
        s+=n/k;
        k*=5;
    }
    return s;
}

int rez(long long a)
{
    for (long long i=a-sqrt(WK); i<=a; i++)
        if (nr0(i)==p)
            return i;
    return -1;
}

int main()
{

    f>>p;
    if (p==0)
    {
        g<<1;
        return 0;
    }
    WK=p*5;
    long long a=1;
    while (a<=WK)
    {
        if (nr0(a)>=p)
        {
            g<< rez(a);
            return 0;
        }
        else a+=sqrt(WK);
    }
}