#include <bits/stdc++.h>
using namespace std;
#define getchar() p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1000000, stdin), p1 == p2) ? EOF : *p1++
char buf[1000000], *p1 = buf, *p2 = buf;
template <typename T>
void read(T &x)
{
    x = 0;
    int f = 1;
    char c = getchar();
    for (; c < '0' || c > '9'; c = getchar())
        if (c == '-')
            f = -f;
    for (; c >= '0' && c <= '9'; c = getchar())
        x = x * 10 + c - '0';
    x *= f;
}
template <typename T, typename... Args>
void read(T &x, Args &...y)
{
    read(x);
    read(y...);
}
template <class T>
void write(T x)
{
    static int stk[30];
    if (x < 0)
        putchar('-'), x = -x;
    int top = 0;
    do
    {
        stk[top++] = x % 10, x /= 10;
    } while (x);
    while (top)
        putchar(stk[--top] + '0');
}
template <class T>
void write(T x, char lastChar) { write(x), putchar(lastChar); }
#define FIO(s)                    \
    freopen(s ".in", "r", stdin); \
    freopen(s ".out", "w", stdout);
template <typename T>
void chkmn(T &x, T y) { x = min(x, y); }
typedef long long ll;
mt19937 rnd(1145141);
int n, m;
ll a[80];
ll b[80];
bitset<80> e[80];
bitset<80> ok;
vector<int> p;
int main()
{
    // FIO("clear");
    read(n, m);
    for (int i = 2; i <= n; i++)
        read(a[i], b[i]);
    while (m--)
    {
        int u, v;
        read(u, v);
        e[u][v] = 1;
    }
    auto dfs = [&](auto self, int u) -> void
    {
        ok[u] = 1;
        if (u != 1)
            p.emplace_back(u);
        for (int v = 1; v <= n; v++)
        {
            if (e[u][v] && !ok[v])
                self(self, v);
        }
    };
    dfs(dfs, 1);
    int T = 40000000;
    ll ans = 1e18;
    while (T--)
    {
        vector<array<int, 2>> vec;
        for (int i = 0; i < (T >= 3e7 ? 9 : T >= 2e7 ? 6
                                                     : 4);
             i++)
        {
            int x = rnd() % p.size();
            int y = rnd() % p.size();
            vec.push_back({x, y});
            swap(p[x], p[y]);
        }
        int t = 0;
        ll w = 0;
        ll mn = 0;
        int lst = 1;
        bool flag = 0;
        ok.reset();
        ok |= e[1];
        for (int i : p)
        {
            if (!ok[i])
            {
                flag = 1;
                break;
            }
            if (lst == 1)
            {
                lst = i;
                w = b[i] - a[i];
                chkmn(mn, -a[i]);
                chkmn(mn, w);
            }
            else
            {
                lst = i;
                chkmn(mn, w - a[i]);
                w += b[i] - a[i];
                chkmn(mn, w);
            }
            ok |= e[i];
        }
        if (!flag && -mn < ans)
        {
            ans = -mn;
        }
        else
        {
            reverse(vec.begin(), vec.end());
            for (auto [x, y] : vec)
                swap(p[x], p[y]);
        }
    }
    write(ans, '\n');
    return 0;
}