No.912 Red-Black Tree
Problem Statement
There is an undirected connected graph consisting of $N$ vertices, $N - 1$ red edges, and $N - 1$ black edges.
The vertices are numbered from $1$ to $N$. The $i$-th red edge connects vertices $A_i$ and $B_i$ bidirectionally, and the $j$-th black edge connects vertices $C_j$ and $D_j$ bidirectionally.
It is guaranteed that the graph consisting only of the red edges and the graph consisting only of the black edges are each connected.
Starting from a vertex of your choice, you will perform the following move some number of times: freely choose one edge connected to the current vertex and move along it to the adjacent vertex.
Red edges never break no matter how many times they are traversed, but a black edge breaks once it is traversed and can no longer be traversed.
Find the minimum number of moves required to break all the black edges.
Input
$N$
$A_1$ $B_1$
$A_2$ $B_2$
$:$
$A_{N-1}$ $B_{N-1}$
$C_1$ $D_1$
$C_2$ $D_2$
$:$
$C_{N-1}$ $D_{N-1}$
- $2 \leq N \leq 2 \times 10^5$
- $1 \leq A_i, B_i \leq N$
- $1 \leq C_j, D_j \leq N$
- The graph consisting only of the red edges and the graph consisting only of the black edges are each connected
- All input values are integers
Output
Output the answer on $1$ line.
Sample
Sample 1
Input
5 1 2 2 3 3 4 3 5 4 2 4 3 4 5 5 1
Output
5
All the black edges can be broken with $5$ moves.
For example, move through the vertices in the order $3 \Rightarrow 4 \Rightarrow 5 \Rightarrow 1 \color{red}{\Rightarrow} \color{black}{2} \Rightarrow 4$. ($\Rightarrow$ denotes a black edge, and $\color{red}{\Rightarrow}$ denotes a red edge.)
Sample 2
Input
4 1 2 2 3 3 4 1 4 4 2 3 2
Output
3
There are cases where no red edge is traversed at all.
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