We can say that x is the largest number.
So the sum is x + (x - 1) + (x - 2) + (x - 3) + (x - 4) = -5
Now solve for x:
x + x + x + x + x - 1 - 2 - 3 - 4 = -5
5x - 10 = -5
5x = 5
x = 1
So the largest number is 1.
Check: 1 + 0 + -1 + -2 + -3 = -2 + -3 = -5 so 1 is correct.