V, E = map(int, input().split())
adj = [[] for i in range(V + 1)]
for i in range(E):
    u, v = map(int, input().split())
    adj[u].append(v)
    adj[v].append(u)
visited = [False] * (V + 1)
ans = []
for i in range(1, V + 1):
    if not visited[i]:
        comp = []
        stack = [i]
        visited[i] = True
        while stack:
            u = stack.pop()
            comp.append(u)
            for v in adj[u]:
                if not visited[v]:
                    visited[v] = True
                    stack.append(v)
        ans.append(comp)
print(len(ans) - 1)
for i in range(len(ans) - 1):
    print(ans[i][0], ans[i+1][0])