#include<iostream.h>
#include<fstream.h>
int n,a,b,c,d;
ifstream f("factorial.in");
ofstream g("factorial.out");
int main () {
    f>>n;
    a=0;
    b=0;
    c=0;
    while ((b<n) || (c<n)) {
          a=a+1;
          if (a%2==0) b=b+1;
          if (a%5==0) {d=a;
                      while ((d%5==0) && (d!=0)) {
                      d=d/5;
                      c=c+1;
                      }}
          }
    if (n!=0) g<<a;
    else g<<1;
}