#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    int k, nr=0, fact=1, i=2, fact2;
    ifstream f("input.in");
    f>>k;
    while (nr<k)
    {
        fact = fact * i;
        fact2 = fact;
        if(fact2 % 10 == 0)
        {
            nr=0;
            while (fact2 % 10 == 0)
            {
                nr++;
                fact2 /= 10;
            }
        }
        i++;
    }
    ofstream g("output.out");
    g<<i-1;

    return 0;
}