#include <bits/stdc++.h>
using namespace std;
typedef long long i64;
const int maxn = 72, n1 = 26;
i64 a[maxn + 5], b[maxn + 5];
i64 f[1 << n1], fr[n1 + 5];
inline bool get(int v, int w) { return (v >> w) & 1; }
int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	for (int i = 2; i <= n; i++) scanf("%lld%lld", &a[i], &b[i]);
	i64 ans;
	if (n <= 26) {
		for (int i = 1; i <= m; i++) {
			int u, v;
			scanf("%d%d", &u, &v);
			fr[v] |= 1 << (u - 1);
		}
		int S = 1 << (n - 1);
		memset(f, 127, sizeof(f));
		f[0] = 0;
		for (int s = 1; s < S; s++)
			for (int i = 2; i <= n; i++)
				if (get(s, i - 2) && ~(s << 1) & fr[i]) f[s] = min(f[s], max(0LL, f[s ^ (1 << (i - 2))] - b[i]) + a[i]);
		ans = f[S - 1];
	}
	printf("%lld", ans);
}