def solve_arc_challenge(grid):
    rows = len(grid)
    cols = len(grid[0])
    changes = 0
    result = [list(row) for row in grid]

    def is_cornered(r, c):
        directions = [(-1,-1),(-1,0),(-1,1),(0,-1),(0,1),(1,-1),(1,0),(1,1)]
        at_symbols = 0
        for dr, dc in directions:
            nr, nc = r + dr, c + dc
            if 0 <= nr < rows and 0 <= nc < cols and grid[nr][nc] == '@':
                at_symbols += 1
        return at_symbols >= 3

    for r in range(rows):
        for c in range(cols):
            if grid[r][c] == 'O' and is_cornered(r, c):
                result[r][c] = 'X'
                changes += 1
                if changes == 3:
                    return [''.join(row) for row in result]

    return result

# Example usage
input_grid = [
"@@OOOOO",
"O@OOOOO",
"OOOOOOO",
"OOOOOOO",
"OOO@OOO",
"OO@@OOO",
"OOOOOOO"
]

output_grid = solve_arc_challenge(input_grid)
for row in output_grid:
    print(row)