#include <stdio.h>
#include <stdlib.h>
FILE *in,*out; long n,P,limdr=1000000000,limst=5,X;

long suma(int x)
{
   long s1=0,pp=5;
    while(x/pp>0)
    {
     s1=s1+x/pp;
     pp=pp*5;
    }
    return s1;

}
long caut (long limst, long limdr)
{ long mij,ss;
mij=(limst+limdr)/2;
     ss=suma(mij);
     if  (ss==P)
            return mij;
            else

    if(limst<limdr)
       {

           if(ss>P)
           return

          caut (limst,mij-1);
          else
        return  caut(mij+1,limdr);

        }
 else return -1;

}

int main()
{
   in=fopen("fact.in","r");
   out=fopen("fact.out","w");
   fscanf(in,"%d",&P);
X=caut(limst,limdr);
while(X%5>0)
X--;
if(P==0)

fprintf(out,"%d",1);

else
fprintf(out,"%ld",X);



   fclose(in);fclose(out);
    return 0;
}