program Kratne2;

{$APPTYPE CONSOLE}

var
i,s,n:integer;
begin
readln(n);
s:=0;
if n>50 then for i:=50 to n do if i mod 2=0 then s:=s+i;
if n<50 then for i:=n to 50 do if i mod 2=0 then s:=s+i;
writeln(s);
readln;
readln;
end.