Given a 2D grid maze representing a maze, where:

• 0 = Empty space (walkable)
• 1 = Wall (impassable)
• 6 = Monster (walkable, but consumes 1 life)

A character starts at (si, sj) and aims to reach (ei, ej). The character has N lives. Find the shortest path from the start to the end, considering the character can walk over at most N-1 monsters.

Constraints:

• Movement is restricted to the 4 cardinal directions (up, down, left, right).
• Return -1 if no path exists.

Example:

maze = [
[0, 0, 1, 0],
[6, 0, 0, 0],
[0, 1, 6, 0],
[0, 0, 0, 0]
]
si, sj = 0, 0
ei, ej = 3, 3
N = 2

# Expected Output: 7