#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <cstring>
#include <map>
#include <cstdlib>
#include <ctime>
#include <cassert>
#include <bitset>
#define f first
#define s second
#define ll long long
#define ull unsigned long long
#define mp make_pair
#define pb push_back
#define vi vector <int>
#define ld long double
#define pii pair<int, int>
#define y1 sda
using namespace std;
const int N = int(3e5), mod = int(1e9)  + 7;
int n,m;
int x[N],y[N],d[N],up[N][18], tin[N], tout[N];

bool used[N];
int ti;
vi g[N];

void dfs(int v,int dep = 0){
	used[v] = 1;
	d[v] = dep;
	tin[v] = ++ti;
	for(int i = 0; i < g[v].size(); i++){
		int to = g[v][i];
		if(!used[to]) {
			up[to][0] = v;
			dfs(to,dep + 1);
		}
	}
	tout[v] = ++ti;
}

bool ok(int u,int v){
	return (tin[u] <= tin[v] && tout[u] >= tout[v]);
}

int lca(int v,int u){
	if(ok(v,u)) return v;
	if(ok(u,v)) return u;
	for(int i = 17; i >= 0; i--){
		if(up[v][i] && !ok(up[v][i],u)) v = up[v][i];
	}
	return up[v][0];
}

int dist(int u,int v){
	return d[u] + d[v] - 2 * d[lca(v,u)];
}


int main () {
	scanf("%d%d",&n,&m);
	for(int i = 1,u,v; i < n; i++){
		scanf("%d%d",&u,&v);
		g[u].pb(v);
		g[v].pb(u);
	}
	dfs(1);
	for(int j = 1; j <= 17; j++){
		for(int i = 1; i <= n; i++) if(up[i][j - 1]){
			up[i][j] = up[up[i][j - 1]][j - 1];
		}
	}

	for(int i = 1; i <= m; i++){
		scanf("%d%d",&x[i],&y[i]);
	}
	int ans = 0;
	int p = 0, _max = 0;
	for(int i = 1; i <= m; i++){
		if(d[x[i]] + d[y[i]] > _max){
			_max = d[x[i]] + d[y[i]];
			p = i;
		}
	}
	for(int i = 1; i <= m; i++){
		ans = max(ans, dist(x[p],x[i]) + dist(y[p],y[i]));
	}
	_max = 0;
	for(int i = 1; i <= m; i++){
		if(dist(x[i],y[i]) > _max){
			_max = dist(x[i],y[i]);
			p = i;
		}
	}
	for(int i = 1; i <= m; i++){
		ans = max(ans, dist(x[p],x[i]) + dist(y[p],y[i]));
	}
	cout << ans;


return 0;
}