#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()
{
   long long int p, s, s1, x,i,t;
   in>>p;
   x=1;
   for(i=1;i<=30;i++) x=x*2;
   t=0;
   for(i=x;i>0;i=i/2)
   {
                     s=t+x; s1=0;
                     while(s!=0)
                     {
                                s1=s1+(s/5);
                                s=s/5;
                     }
                     if(s1<t)
                     {
                             t=t+x;
                     }                     
   }
   out<<t;
  return 0;
}