#include <fstream>

using namespace std;
int prod, i, j, nrZero, p;

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

int main () {
    fin>>p;
    for (i=1;;i++) {
        /// cati de 0 are la final i!

        prod = 1;
        for (j=1;j<=i;j++)
            prod *= j;
        nrZero = 0;
        while (prod%10 == 0) {
            nrZero++;
            prod /= 10;
        }

        if (nrZero == p)
            break;
    }
    fout<<i;
}