#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{
    int fact,k,x,p;
    f>>p;
    fact=1;
    k=0;
    for(x=2;x<=p*5&&k<p;x++)
        {
            fact=fact*x;
            while(fact%10==0)
              {
                  k++;
                  fact=fact/10;
              }
        if(fact>1000) fact=256;
        }
       g<<x-1;
       f.close();
       g.close();

    return 0;
}