#include <iostream>
#include <fstream>
#include <limits.h>
using namespace std;

int cifre0(int n)
{
    int nr = 0;
    for (int i=5; n/i>=1; i*=5)
        nr += n / i;
    return nr;
}

int main()
{
    ifstream f("factorial.in");
    ofstream g("fact.out");
    int p;
    f>>p;
    int st = 0, dr = INT_MAX;
    while(st <= dr)
    {
        int m = (st + dr) / 2;
        if(cifre0(m) == p)
        {
            g<<m / 5 * 5;
            return 0;
        }
        else if(cifre0(m) > p)
            dr = m - 1;
        else
            st = m + 1;
    }
    g<<-1;
    return 0;
}