def is_safe(board, row, col):
    for i in range(row):
        if board[i] == col or \
           board[i] - i == col - row or \
           board[i] + i == col + row:
            return False
    return True

def solve_n_queens_util(board, row, N, solutions):
    if row == N:
        solutions.append(board[:])
        return
    for col in range(N):
        if is_safe(board, row, col):
            board[row] = col
            solve_n_queens_util(board, row + 1, N, solutions)

def solve_n_queens(N):
    solutions = []
    solve_n_queens_util([0] * N, 0, N, solutions)
    return [['.' * col + 'Q' + '.' * (N - col - 1) for col in solution] for solution in solutions]

# Example: Solve the 4-Queens problem
N = 4
solutions = solve_n_queens(N)
for i, solution in enumerate(solutions):
    print(f"Solution {i+1}:")
    for row in solution:
        print(row)
    print()