edges = []
vertices = []

def DFS(vertex: tuple):
    vertex[1] = True
    for edge in edges:
        if edge[0] == vertex[0]:
            v = vertices[edge[1] - 1]
            if not v[1]:
                DFS(v)
        if edge[1] == vertex[0]:
            v = vertices[edge[0] - 1]
            if not v[1]:
                DFS(v)

def main():
    verts = set()
    f = open('friends.in')
    f.readline() # skipping first line
    for line in f:
        edge = list(map(int, line.split()))
        edges.append(edge)
        verts.add(edge[0])
        verts.add(edge[1])

    for vertex in verts:
        vertices.append([vertex, False])

    k = 0
    nodes = []
    for vertex in vertices:
        if not vertex[1]:
            DFS(vertex)
            nodes.append(vertex[0])
            k += 1

    print(k - 1)
    if not k == 1:
        for i, node in enumerate(nodes[:-1]):
            print('%d %d' % (nodes[i], nodes[i + 1]))
main()