#include <fstream>


int main()
{
    std::ifstream f("factorial.in");
    std::ofstream g("factorial.out");

    int zeroes, i = 1;
    f >> zeroes;
    if (!zeroes) {
        g << 1 << "\n";
        return 0;
    }

    while (zeroes) {
        if (i % 5) {
            zeroes --;
        }
        else {
            zeroes -= 2;
        }
        i++;
    }

    g << (i-1) * 5 << "\n";
}