#include<fstream>  
 using namespace std;  
 int main()  
 {  
     ifstream in ("fact.in");  
     ofstream out("fact.out");  
     long int p,nrtz,i,ii;  
     in>>p;  
     nrtz=5*p;  
     for (i=25;i<=nrtz;i+=25)  
     {ii=i/5;  
      while(ii%5==0)  
     { nrtz=nrtz-5;  
       ii=ii/5;  
     }  
     }  
     if (nrtz==0) nrtz =1;  
     out<< nrtz;  
     in.close();  
     out.close();  
     return 0;  
}