#include <iostream>
#include <chrono>
#include <fstream>

using namespace std::chrono;

std::ifstream f1("fact.in");
std::ofstream f2("fact.out");


int pof(int t) {
    if (t % 5 == 0) {
        return 1 + pof(t / 5);
    }
    return 0;
}

void factorial() {
    int target;

//    std::ifstream f1(stdin);
//    std::ofstream f2(stdout);

    f1 >> target;

    {
        int counter = 0;
        while (target > 0) {
            counter += 5;
            target -= pof(counter);
        }
        f2 << counter << std::endl;
    }
}

int main() {
    auto start = high_resolution_clock::now();

    factorial();

    auto stop = high_resolution_clock::now();
    auto duration = duration_cast<milliseconds>(stop - start);
    std::cout << std::endl << "[time]:" << duration.count() << std::endl;
    return 0;
}