#include <fstream>

using namespace std;

int main()
{
    int n,p,k,a,l,h,sol;

    ifstream fin("fact.in");
    fin>>p;
    fin.close();

    sol = -1;
    l = 1;
    h = 2000000000;
    while(l<=h)
    {
        n=(l+h)/2;
        k = 0;
        for (a = 5;a <= n; a *= 5)
            k = k + n / a;
        if (k == p)
            {
                sol = n;
                h = n - 1;
            }
        else if (k > p) h = n - 1;
        else l = n + 1;
    }

    ofstream fout("fact.out");
    fout<<sol;
    fout.close();

    return 0;
}