#include <iostream>
#include <fstream>

using namespace std;

int n2,n5,n,i,ii;

int main()
{
    ifstream f ("factorial.in");
    ofstream g ("factorial.out");
    f>>n;
    if(n==0)g<<1;
    else
    {
      while(n2<n||n5<n){
        i++;
        ii=i;
        while(ii%2==0){n2++;ii/=2;}
        ii=i;
        while(ii%5==0){n5++;ii/=5;}
      }
      g<<i;
    }
    f.close ();
    g.close ();
    return 0;
}