#include <bits/stdc++.h>
using namespace std;
using ll=long long;
template<typename T>
ll SZ(const T &a){
	return a.size();
}
constexpr ll N=200010;
constexpr ll inf=1e18;
ll sub,n,a[N],fa[N];
vector<ll> T[N];
void dfs(ll u){
	for(ll v:T[u]){
		fa[v]=u;
		T[v].erase(find(T[v].begin(),T[v].end(),u));
		dfs(v);
	}
}
int main(){
	ios::sync_with_stdio(0),cin.tie(0);
	cin>>sub>>n;
	for(ll i=1;i<=n;i++){
		cin>>a[i];
	}
	T[0].push_back(1);
	for(ll i=1,u,v;i<n;i++){
		cin>>u>>v;
		T[u].push_back(v);
		T[v].push_back(u);
	}
	dfs(1);
	ll s=0;
	a[0]=-inf;
	while(1){
		ll rt=0;
		for(ll u=1;u<=n;u++){
			if(SZ(T[u])){
				ll ok=1;
				for(ll v:T[u]){
					if(SZ(T[v])){
						ok=0;
						break;
					}
				}
				if(ok){
					rt=u;
					break;
				}
			}
		}
		if(!rt){
			break;
		}
		ll son=rt;
		for(ll u:T[rt]){
			if(a[u]>a[son]){
				son=u;
			}
		}
		if(son==rt){
			for(ll u:T[rt]){
				fa[u]=fa[rt];
				T[fa[u]].push_back(u);
			}
			T[rt].clear();
			continue;
		}
		a[rt]-=a[son];
		T[rt].erase(find(T[rt].begin(),T[rt].end(),son));
		if(!SZ(T[rt])){
			s+=a[rt];
			T[fa[rt]].erase(find(T[fa[rt]].begin(),T[fa[rt]].end(),rt));
			continue;
		}
		son=0;
		for(ll u:T[rt]){
			if(a[u]>a[son]){
				son=u;
			}
		}
		a[rt]+=a[son];
		T[rt].erase(find(T[rt].begin(),T[rt].end(),son));
	}
	sort(T[0].begin(),T[0].end(),[&](ll u,ll v)->ll{
		return a[u]>a[v];
	});
	ll o=1,ans=0;
	for(ll u:T[0]){
		ans+=o*a[u];
		o=-o;
	}
	ans+=o*s;
	cout<<ans<<"\n";
	return 0;
}