function solution(arr) {
  if (arr[0] == 1) return 0;

  let i = 1;
  for (; i < arr.length && arr[i] == 0; i *= 2) {}

  let left = Math.floor(i / 2) + 1;
  let right = i >= arr.length ? arr.length - 1 : i;
  let mid = -1;

  while (left <= right) {
    mid = Math.ceil((right - left) / 2 + left);
    if (arr[mid] == 1 && arr[mid - 1] == 0) return mid;
    else if (arr[mid] == 0) left = mid + 1;
    else right = mid - 1;
  }

  return -1;
}

const arr = [0, 1, 1, 1, 1];
console.log(solution(arr));