C++ :

#include<iostream>
#include<vector>

using namespace std;

const int N = 1e6 + 10;
int n, q, u, v, a[N], fa[N][20], dep[N], cnt;
vector<int> g[N];

void dfs(int u, int f){
	fa[u][0] = f;
	dep[u] = dep[f] + 1;
	for(int i = 1; i < 20; i++) fa[u][i] = fa[fa[u][i-1]][i-1];
	for(int v: g[u]){
		if(v == f) continue;
		dfs(v, u);
	}
}

int lca(int u, int v){
	if(dep[u] < dep[v]) swap(u, v);
	for(int i = 19; i >= 0; i--){
		if((dep[u] - dep[v]) & (1 << i)) u = fa[u][i];
	}
	if(u == v) return u;
	for(int i = 19; i >= 0; i--){
		if(fa[u][i] != fa[v][i]) u = fa[u][i], v = fa[v][i];
	}
	return fa[u][0];
}

void get_ans(int u, int f){
	for(int v: g[u]){
		if(v == f) continue;
		get_ans(v, u);
		a[u] += a[v];
	}
}

int main(){
	cin >> n >> q;
	for(int i = 1; i < n; i++){
		cin >> u >> v;
		g[u].push_back(v);
		g[v].push_back(u);
	}
	dfs(1, 0);
	while(q--){
		cin >> u >> v;
		int w = lca(u, v);
		a[u]++; a[v]++;
		a[w]--; a[fa[w][0]]--;
	}
	get_ans(1, 0);
	cin >> u >> v;
	int w = lca(u, v);
	while(u != w){
		if(a[u] == 0) cnt++;
		u = fa[u][0];
	}
	while(v != w){
		if(a[v] == 0) cnt++;
		v = fa[v][0];
	}
	if(a[u] == 0) cnt++;
	cout << cnt;
	return 0;
}