class Graphe:
    def __init__(self):
        self.sommets = {}

    def edge(self, u, v):
        if v not in self.sommets:
            self.sommets[v] = []
        if u not in self.sommets:
            self.sommets[u] = []
        self.sommets[u].append(v)
        self.sommets[v].append(u)