x86 - Assembly, easy code, Segmentation fault why -

i wrote first assembly code, tried copy easy c++ operation. values good, run ending segmentation fault. why?

;int x = 10; ;int y = 20; ;x += y; ;cout<<x<<"\n";   ;********************* global main extern readln extern println  section .data x dd 10 y dd 20  section .txt  main: ; second arg eax mov eax, [y]  push eax  ; first arg eax mov eax, [x]  pop ebx add eax, ebx  push eax call println add esp, 4