var nr,m,p,x:longint;
begin
assign(input,'fact.in');reset(input);
assign(output,'fact.out');rewrite(output);
readln(p);
nr:=5;
m:=1;
 while p<>m do begin
 if nr mod 25=0 then begin
    x:=nr;
  while (p<>m) and (x mod 5=0) do
     x:=x div 5;
     inc(nr,5);
     inc(m); end
 else
  inc(nr,5);
  inc(m); end;
write(nr);
close(input);close(output);
end.