#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 1000;

ll n, m;
ll a[N], b[N], c[N];
bool vis[N], st[N];
vector<ll> G[N];
vector<int> tmp;

void init() {
    for (int i = 0; i <= N - 1; i++)
        vis[i] = st[i] = false;
    tmp.clear();
    return;
}

bool dfs(ll x, ll hp) {
    vis[x] = true;
    for (auto i : G[x]) {
        if (vis[i])
            continue;
        tmp.push_back(i);
        vis[i] = true;
    }
    ll id = -1, maxn = -1e18;
    bool flag = false;
    for (int i = 0; i < tmp.size(); i++) {
        if (!st[i])
            flag = true;
        if (c[tmp[i]] > maxn && hp >= a[tmp[i]] && !st[i]) {
            id = i;
            maxn = c[tmp[i]];
        }
    }
    st[id] = true;
    if (id == -1)
        return flag ^ 1;
    return dfs(tmp[id], hp + maxn);
}

void solve() {
    cin >> n >> m;
    for (int i = 2; i <= n; i++) {
        cin >> a[i] >> b[i];
        c[i] = b[i] - a[i];
    }
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        G[u].push_back(v);
    }
    ll l = 0, r = 1e18;
    while (l < r) {
        ll mid = l + r >> 1;
        init();
        if (dfs(1, mid))
            r = mid;
        else
            l = mid + 1;
    }
    cout << l << '\n';
    return;
}

int main() {
    ios::sync_with_stdio(0);
    solve();
    return 0;
}