program csn_csc;
var a,b,c,d:integer;
begin
write('moi ban nhap so thu nhat:');readln(a);
write('moi ban nhap so thu hai:');readln(b);
write('moi ban nhap so thu ba:');readln(c);
write('moi ban nhap so thu tu:');readln(d);
if (b-a=c-b) and (c-b=d-c) then write('day la cap so cong') else if (b/a=c/b) and (c/b=d/c) then write('day la cap so nhan') else write('day khong la cap so cong va khong la cap so nhan');
readln;
end.