#include<bits/stdc++.h>
using namespace std;
const int N=100;
using ll=long long;
int n,m;
ll a[N+5],b[N+5];
bool used[N+5];
vector<int> e[N+5];
bool chk(ll x){
    for(int i=1;i<=n;i++)
        used[i]=0;
    used[1]=1;
    while(1){
        bool ok=1;
        for(int i=1;i<=n;i++)
            if(!used[i]) ok=0;
        if(ok) return 1;
        int mx=-1;
        for(int i=1;i<=n;i++)
            if(used[i])
                for(auto v:e[i])
                    if(!used[v]&&a[v]<=x)
                        if(mx==-1||b[v]>b[mx]) mx=v;
        if(mx==-1) return 0;
        x+=b[mx]; used[mx]=1;
    }
}
int main(){
    scanf("%d %d",&n,&m);
    for(int i=2;i<=n;i++){
        scanf("%lld %lld",&a[i],&b[i]);
        b[i]-=a[i];
    }
    for(int i=1,u,v;i<=m;i++){
        scanf("%d %d",&u,&v);
        e[u].push_back(v);
    }
    ll l=1,r=1ll<<60;
    while(l<=r){
        ll mid=l+r>>1;
        if(chk(mid)) r=mid-1;
        else l=mid+1;
    }
    printf("%lld\n",l);
    return 0;
}