var p,p1,p2,p3,p4,p5,p6,p7,p8,p9,p0,nr,k:longint;
 g,f:text;
 begin
   assign(f,'fact.in');reset(f);
   assign(g,'fact.out');rewrite(g);
   read(f,p);
   nr:=p*5;
   p:=p-(p mod 5);
   p1:=(p div 5)*5;
   p2:=(p div 25);
   p3:=(p div 125)*5;
   p4:=(p div 625)*5;
   p5:=(p div 3125)*5;
   p6:=(p div 15625)*5;
   p7:=(p div 78125)*5;
   p8:=(p div 390625)*5;
   p9:=(p div 1953125)*5;
   p0:=(p div 9765625)*5;
   if p<>0 then begin
       nr:=p1+p2+p3+p4+p5+p6+p7+p8+p9+p0;
    end;
   write(g,nr);
   close(f);
   close(g);
 end.