#include <bits/stdc++.h>
using namespace std;
#define fr(i,j,k) for(int i=j;i<=k;++i)
#define N 45
#define M (1<<25)+5
#define ll long long
#define pb push_back
int n,m;
void W(ll &x,ll y) {x=min(x,y);}
namespace Sub1
{
	int rt[N];ll ans=1e18,a[N],b[N];vector<int> e[N];
	void dfs()
	{
		int u=0;vector<int> vc;
		for(int i=2;i<=n;++i) if(rt[i]==i)
		{
			if(!u) {u=i;continue;}
			if(a[i]<=b[i]) {if(a[u]>b[u] || a[i]<a[u]) u=i;}
			else if(a[u]>b[u] && b[i]>b[u]) u=i;
		}if(!u) {ans=min(ans,a[1]);return;}
		for(auto v:e[u])
		{
			v=rt[v];ll tA=a[v],tB=b[v];vc.clear();
			for(int i=2;i<=n;++i) if(rt[i]==u) rt[i]=v,vc.pb(i);
			if(a[u]<b[v]) b[v]-=a[u]-b[u];else a[v]+=a[u]-b[v],b[v]=b[u];
			dfs();a[v]=tA;b[v]=tB;for(auto i:vc) rt[i]=u;
		}
	}
	void slv()
	{
		for(int i=1;i<=n;++i) rt[i]=i;
		for(int i=2;i<=n;++i) scanf("%lld %lld",&a[i],&b[i]);
		for(int i=1,u,v;i<=m;++i) scanf("%d %d",&u,&v),e[v].pb(u);
		dfs();printf("%lld\n",ans);
	}
}
namespace Sub2
{
	const int Maxn=70,Maxs=(1<<26)+10;
    const ll inf=1e18;
    ll f[Maxs];
    int ed[Maxn];
    ll a[Maxn],b[Maxn];
    inline void chkmin(ll &x,ll y){if(x>y) x=y;}
    inline void work(){
        fr(i,2,n) scanf("%lld%lld",&a[i],&b[i]);
        fr(i,1,m){int x,y;cin>>x>>y;ed[y]|=(1<<(x-1));}
        int S=(1<<(n-1))-1;
        fr(i,1,S) f[i]=inf;
        fr(i,0,S){
            int tr=i*2+1;
            ll now=0;
            fr(id,2,n) if(i&(1<<(id-2))) now+=b[id]-a[id];
            fr(id,2,n) if(ed[id]&tr) chkmin(f[i+(1<<(id-2))],max(f[i],a[id]-now));
        }
        printf("%lld\n",f[S]);
    }
}
int main()
{
	scanf("%d %d",&n,&m);
	if(n>26) Sub1::slv();else Sub2::work();return 0;
}