#include <fstream>
#include <iostream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int p;

long long cate(long long n)
{
    long long a, b;
    a = b = 0;
    for(long long k = 1; k <= n; ++k)
    {
        if(!(k % 2))
            ++a;
        if(!(k % 5))
            ++b;
    }
    return (a <= b ? a : b);
}

int main()
{
    in >> p;
    for(long long i = 1;; ++i)
    {
        if(cate(i) == p)
        {
            out << i;
            return 0;
        }
    }
    return 0;
}