#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int p;
    f>>p;
    int numar,i;
    numar=1;  i=1;

    int k=0;
    int zero=1;
    //cati de zero la sfarsit
    while(k!=p)
    {
        zero=zero*10;
        k++;
    }
    do
    {
        numar=numar*i;
        i++;
    }while(numar%zero!=0);
    i--;
    g<<i;

    return 0;
}