#include <bits/stdc++.h>
using namespace std;
const int maxN = (int)5e3 + 3;
vector<int> g[maxN], p[maxN];
int u, v, cur_h[maxN], cnt, n;
bool used[maxN], dp[maxN], ans[maxN];
void dfs(int v, int* cur_h) {
  used[v] = true;
  cur_h[v] = 1;
  for (int i = 0; i < (int)g[v].size(); ++i) {
    int to = g[v][i];
    if (!used[to]) {
      p[v].push_back(to);
      dfs(to, cur_h);
      cur_h[v] += cur_h[to];
    }
  }
}
void init_arrays() {
  memset(dp, 0, sizeof(bool) * maxN);
  memset(used, 0, sizeof(bool) * maxN);
  memset(cur_h, 0, sizeof(int) * maxN);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  for (int i = 0; i < n - 1; ++i) {
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  init_arrays();
  dfs(1, cur_h);
  dp[0] = 1;
  for (int i = 1; i <= n; ++i) {
    for (int k = 1; k <= n; ++k) dp[k] = 0;
    for (int j = 0; j < (int)p[i].size(); ++j)
      for (int k = n; k >= 0; --k) dp[k + cur_h[p[i][j]]] |= dp[k];
    for (int k = n; k >= 0; --k) dp[k + n - cur_h[i]] |= dp[k];
    for (int k = n; k >= 0; --k) ans[k] |= dp[k];
  }
  --n;
  for (int i = 1; i < n; ++i)
    if (ans[i] == true) ++cnt;
  cout << cnt << endl;
  for (int i = 1; i < n; ++i)
    if (ans[i] == true) cout << i << ' ' << n - i << endl;
  return 0;
}
