def eulerPath(graph):
    # counting the number of vertices with odd degree
    odd = [ x for x in graph.keys() if len(graph[x])&1 ]
    odd.append( graph.keys()[0] )

    if len(odd)>3:
        return None

    stack = [ odd[0] ]
    path = []

    # main algorithm
    while stack:
        v = stack[-1]
        if graph[v]:
            u = graph[v][0]
            stack.append(u)
            # deleting edge u-v
            del graph[u][ graph[u].index(v) ]
            del graph[v][0]
        else:
            path.append( stack.pop() )

    return path