#include<fstream>
#include<iostream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int P,cifre,N=1,k;

int main()
{
    f>>P;
    while (cifre<P)
    {
        k=5;
        while (true)
        {
            if (N%k==0)
                cifre++;
            else
                break;
            k*=5;
        }
        N++;
    }
    g<<--N;
    f.close();g.close();
    return 0;
}