#include <iostream>
#include <fstream>

using namespace std;

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

    bool two = false, five = false;
    int i = 0,nrZero = 0;
    long long p;
    in >> p;
    while(nrZero != p)
    {
        i++;
        if(i % 10 == 2) two = true;
        if(i % 10 == 5) five = true;
        if(i % 10 == 0) nrZero ++;
        if(two == true && five == true) {nrZero ++; two = false; five = false;}
    }
    out << i;
}