2048 is a game where you need to slide numbered tiles (natural powers of 2) up, down, left or right on a square grid to combine them in a tile with the number 2048.

The sliding procedure is described by the following rules:

• Tiles slide as far as possible in the chosen direction until they are stopped by either another tile or the edge of the grid.
• If two tiles of the same number collide while moving, they will merge into a tile with the total value of the two tiles that collided.
  • If more than one variant of merging is possible, move direction shows one that will take effect.
• Tile cannot merge with another tile more than one time.

Sliding is done almost the same for each direction and for each row/column of the grid, so your task is to implement only the left slide for a single row.

Examples

leftSlide({2, 2, 2, 0}) ➞ {4, 2, 0, 0}
// Merge left-most tiles first

leftSlide({2, 2, 4, 4, 8, 8}) ➞ {4, 8, 16, 0, 0, 0}
// Only merge once

leftSlide({0, 2, 0, 2, 4}) ➞ {4, 4, 0, 0, 0}

leftSlide({0, 2, 2, 8, 8, 8}) ➞ {4, 16, 8, 0, 0, 0}

Notes

• Input row can be of any size (empty too).
• Input row will contain only natural powers of 2 and 0 for empty tiles.
• Keep trailing zeros in the output.