#include <iostream>
#include <fstream>

using namespace std;

long long count_zeros(long long n) {
    long long zeros = 0;
    for (long long i = 5; n / i >= 1; i *= 5) {
        zeros += n / i;
    }
    return zeros;
}

long long find_N(long long p) {
    if (p == 0) return 1;
    
    long long low = 1;
    long long high = 5 * p;
    long long ans = -1;

    while (low <= high) {
        long long mid = low + (high - low) / 2;
        long long zeros = count_zeros(mid);

        if (zeros >= p) {
            if (zeros == p) {
                ans = mid;
            }
            high = mid - 1;
        } else {
            low = mid + 1;
        }
    }

    return ans;
}

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

    long long P;
    if (fin >> P) {
        long long N = find_N(P);
        fout << N << endl;
    }
    return 0;
}