#include <iostream>
#include <fstream>

using namespace std;

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

long long nr_de_zerouri(long long n);

int main()
{
    long long p;
    fin >> p;
    long long n = -1;
    long long l = 1,r = 100000000,m,k;
    while(l <= r)
    {
        m = (l + r) / 2;
        k = nr_de_zerouri(m);
        if(k == p)
        {
            n = m;
            break;
        }
        else if(k > p)
        {
            r = m - 1;
        }
        else
        {
            l = m + 1;
        }
    }
    if(n != -1)
    {
        fout << n - n % 5;
    }
    else
    {
        fout << n;
    }
    fin.close();
    fout.close();
    return 0;
}

long long nr_de_zerouri(long long n)
{
    long long nr = 0;
    for(long long i = 5; n / i >= 1; i *= 5)
    {
        nr += n / i;
    }
    return nr;
}