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

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

int P;
int check = 0;

int cutz(int s);

int main()
{
    is >> P;
    int rez = 1;
    int N = 0;
    while(check < P)
    {
        N++;
        rez = rez * N;
        rez = cutz(rez);
    }
    os << N;
    is.close();
    os.close();
    return 0;
}
int cutz(int s)
{
    if(s > 10000)
        s = s % 10000;
    if(s % 10 == 0)
    {
        check = check + 1;
        s = s / 10;
    }
    return s;
}