def minimax(matrix):
    candidates = list(matrix.keys())
    worst_defeats = {}

    for candidate in candidates:
        worst_defeat = float('inf')
        for opponent in candidates:
            if candidate != opponent:
                margin = matrix[opponent][candidate] - matrix[candidate][opponent]
                worst_defeat = min(worst_defeat, -margin)
        worst_defeats[candidate] = worst_defeat

    return max(worst_defeats, key=worst_defeats.get)