Find an algorithm for writing any positive integer in negabinary, i.e., as a sum of powers of -2.

For example,

7 = 11011 = (-2)^4 + (-2)^3 + (-2)^1 + (-2)^0
19 = 10111 = (-2)^4 + (-2)^2 + (-2)^1 + (-2)^0