var f : text;
   p,n,k,i,x : longint;
begin
     assign(f,'fact.in'); reset(f);
     readln(f,p);
     close(f);  n:=0; k:=5;
     while i<p do
           begin
                x:=k;
                repeat i:=i+1; n:=n+5; x:=x div 5;   until x mod 5<>0;
                k:=k+5;
           end;
     if p=0 then n:=1;
     assign(f,'fact.out'); rewrite(f);
     write(f,n);
     close(f);
end.