It is known that the solution x.y of the equations x + 2Y = m, 2x + y = m + 1 satisfies x + y ≥ 0, then the value range of M is

It is known that the solution x.y of the equations x + 2Y = m, 2x + y = m + 1 satisfies x + y ≥ 0, then the value range of M is

X+2Y=M,2X+Y=M+1
Add
3X+3Y=2M+1
3*(X+Y)=2M+1≥0
M≥-1/2