#include <stdio.h>
#include <vector>
#include <algorithm>
#include <cassert>
std::vector<int> AdjList[500005];
std::vector<int> Leaf;
int Root;
int H[500005];
int Pa[500005][20];
void dfs(int u, int pa, int h)
{
H[u] = h;
Pa[u][0] = pa;
if (pa == 0)
Root = u;
int i, v, s = AdjList[u].size();
for (i = 0; i < s; i++)
{
v = AdjList[u][i];
if (v != pa)
{
dfs(v, u, h + 1);
}
}
if (s == 1)
Leaf.push_back(u);
}
int cnt;
int M[500005];
int lca(int u, int v)
{
int i;
if (H[v] > H[u])
return lca(v, u);
if (H[u] > H[v])
{
for (i = 19; i >= 0; i--)
{
if (H[Pa[u][i]] > H[v])
u = Pa[u][i];
}
u = Pa[u][0];
}
if (u == v)
return u;
for (i = 19; i >= 0; i--)
{
if (Pa[u][i] != Pa[v][i])
{
u = Pa[u][i];
v = Pa[v][i];
}
}
u = Pa[u][0];
return u;
}
void mark(int u, int v)
{
// printf("mark u%d v%d lca%d\n", u, v, lca(u, v));
M[u]++;
M[v]++;
M[lca(u, v)] -= 2;
}
void dfscheck(int u, int pa)
{
int i, v, s = AdjList[u].size();
for (i = 0; i < s; i++)
{
v = AdjList[u][i];
if (v != pa)
{
dfscheck(v, u);
M[u] += M[v];
}
}
// printf("M[%d] = %d\n", u, M[u]);
assert(M[u] >= 0);
if (M[u] == 0 && pa != 0) cnt++;
}
int N;
int check()
{
int i, j;
for (i = 1; i <= N; i++)
M[i] = 0;
cnt = 0;
for (i = 0, j = Leaf.size() - 1; i < j; i++, j--)
mark(Leaf[i], Leaf[j]);
if (i == j)
mark(Leaf[i], Root);
if (AdjList[1].size() > 1)
dfscheck(1, 0);
else
dfscheck(AdjList[1][0], 0);
return (cnt == 0);
}
int main()
{
scanf("%d", &N);
int i, j, u, v;
for (i = 0; i < N - 1; i++)
{
scanf("%d %d", &u, &v);
AdjList[u].push_back(v);
AdjList[v].push_back(u);
}
if (AdjList[1].size() > 1)
dfs(1, 0, 0);
else
dfs(AdjList[1][0], 0, 0);
for (j = 1; j < 20; j++)
{
for (i = 1; i <= N; i++)
{
Pa[i][j] = Pa[Pa[i][j - 1]][j - 1];
}
}
printf("%d\n", (Leaf.size() + 1)/2);
// if (check())
// {
// for (i = 0, j = Leaf.size() - 1; i < j; i++, j--)
// printf("%d %d\n", Leaf[i], Leaf[j]);
// if (i == j)
// printf("%d %d\n", Leaf[i], Root);
// }
// else
// {
// Leaf.push_back(Leaf[0]);
// Leaf.erase(Leaf.begin());
// if (!check())
// assert(1 == 0);
// for (i = 0, j = Leaf.size() - 1; i < j; i++, j--)
// printf("%d %d\n", Leaf[i], Leaf[j]);
// if (i == j)
// printf("%d %d\n", Leaf[i], Root);
// }
int cnt = 0;
while (!check())
{
if (Leaf.size() < 10)
std::next_permutation(Leaf.begin(), Leaf.end());
else
{
Leaf.push_back(Leaf[0]);
Leaf.erase(Leaf.begin());
}
}
if (cnt == Leaf.size())
assert(1 == 0);
for (i = 0, j = Leaf.size() - 1; i < j; i++, j--)
printf("%d %d\n", Leaf[i], Leaf[j]);
if (i == j)
printf("%d %d\n", Leaf[i], Root);
}
