adj = ((0, 0), (-1, 0), (1, 0), (0, -1), (0, 1))
def detonate(grid, t, i, j):
    return any(t - grid[i + x][j + y] == 3 for x, y in adj if i + x >= 0 and j + y >= 0 and i + x < len(grid) and j + y < len(grid[0]))
    
def bomberMan(n, grid):
    n = min(n, 2 + (n-2) % 4)
    grid = [[('.', 0)[c == 'O'] for c in r] for r in grid]
    
    for t in range(2, n+1, 2):
        grid = [[t if c == '.' else c for c in r] for r in grid]
        if t+1 <= n:
            grid = [['.' if detonate(grid, t+1, i, j) else grid[i][j] for j in range(len(grid[i]))] for i in range(len(grid))]
    
    return [''.join(('O', '.')[c == '.'] for c in r) for r in grid]