#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p;
int cautare_binara(int x)
{
    int st = 1, dr = 5*p+5, sol = -1;
    while(st <= dr)
    {
        int nr = 0;
        int m = (st + dr) / 2;
        for(int i = 5; i <= m; i *= 5)
            nr += m / i;
        if(p == nr)
            sol = m;
        if(nr < p)
            st = m + 1;
        else
            dr = m - 1;
    }
        return sol;
}
int main()
{
   fin >> p;
   fout << cautare_binara(p);
    return 0;
}