Find out from which index you will leave the matrix at the end

Given a matrix with 0’s and 1’s, you enter the matrix at cell (0,0) in left to the right direction. whenever you encounter a 0 you retain in the same direction, if you encounter a 1’s you have to change direction to the right of current direction and change that 1 value to 0, you have to find out from which index you will leave the matrix at the end.