#include <fstream>
using namespace std;

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

long long zerouri(long long n) {
    long long cnt = 0;

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

    return cnt;
}

int main() {
    long long P;
    fin >> P;

    long long st = 1;
    long long dr = 5 * (P + 1);
    long long raspuns = -1;

    while (st <= dr) {
        long long mij = st + (dr - st) / 2;

        long long z = zerouri(mij);

        if (z >= P) {
            if (z == P)
                raspuns = mij;

            dr = mij - 1;
        } else {
            st = mij + 1;
        }
    }

    fout << raspuns;

    return 0;
}