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