uses crt;
var a,b,c,d:integer;
begin
clrscr;
write('-> ');
readln(a,b,c,d);
if (a=b) and (b=c) then write(d) else
if (a=c) and (c=d) then write(b) else
if (a=b) and (b=d) then write(c) else write(a);
readln;
end.
uses crt;
var a,b,c,d:integer;
begin
clrscr;
write('-> ');
readln(a,b,c,d);
if (a=b) and (b=c) then write(d) else
if (a=c) and (c=d) then write(b) else
if (a=b) and (b=d) then write(c) else write(a);
readln;
end.