program ss;
var z,j,i,p:int64;
f:text;
begin
 assign(f,'fact.in'); reset(f);
 readln(f,p);
 close(f);
 assign(f,'fact.out'); rewrite(f);
 j:=0;
 z:=0;
 repeat
  j:=j+1;
  i:=j;
  while (i mod 5=0) do begin
   z:=z+1;
   i:=i div 5;
  end;

 until p=z;
 write(f,j); close(f);
end.