#include <fstream>

int zeros(int n) {
    int res = 0;
    while ((n = n / 5)) {
        res += n;
    }
    return res;
}

void factorial() {
    std::ifstream f1;
    std::ofstream f2;

    int target;

    f1.open("fact.in");
    f2.open("fact.out");

    f1 >> target;

    int start = 1;
    int end = 400000015;
    int number_of_zeroes;
    int half;

    do {
        half = (start + end) / 2;
        number_of_zeroes = zeros(half);
        if (number_of_zeroes >= target) {
            end = half;
        } else if (number_of_zeroes < target) {
            start = half + 1;
        }
    } while (start != end);

    if (zeros(start) == target) {
        f2 << start;
    } else {
        f2 << -1;
    }
}


int main() {
    factorial();
}