#include <fstream>

using namespace std;

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

int main()
{
    int Nr, rez = -1;
    fin >> Nr;
    int st = 0, dr = 400000015;
    while(st <= dr)
    {
        int mijl = st + (dr - st)/2, exp = 0, div = 5;
        while(mijl >= div)
        {
            exp += mijl/div;
            div *= 5;
        }
        if(exp > Nr)
            dr = mijl - 1;
        if(exp < Nr)
            st = mijl + 1;
        if(exp == Nr)
        {
            rez = mijl;
            dr = mijl - 1;
        }
    }
    fout << rez;
    return 0;
}