#include <fstream>
using namespace std;

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

    int P;
    fin >> P;
    if (P == 0) {
        fout << 1 << "\n";
        return 0;
    }
long long st = 1, dr = 1e18, rasp = -1;

    while (st <= dr) {
        long long mid = (st + dr) / 2;
        long long n = mid, cnt = 0;


    while (n > 0) {
            cnt += n / 5;
            n /= 5;
        }

        if (cnt == P) {
            rasp = mid;
            dr = mid - 1; //
        } else if (cnt < P) {
            st = mid + 1;
        } else {
            dr = mid - 1;
        }
    }

    fout << rasp << "\n";
    return 0;
}