#include<bits/stdc++.h>
#define ll long long
#define fr(i,j,k) for(register int i=j;i<=k;++i)
#define rf(i,j,k) for(register int i=j;i>=k;--i)
#define foredge(i,j) for(register int i=head[j];i;i=e[i].nxt)
#define pb push_back
#define Times printf("Time:%.3lf\n",clock()/CLOCKS_PER_SEC)
#define pii pair<int,int>
#define mk make_pair
using namespace std;
inline int read(){
	int x=0;
	bool f=0;
	char c=getchar();
	while(!isdigit(c)) f|=(c=='-'),c=getchar();
	while(isdigit(c)) x=(x<<3)+(x<<1)+(c^48),c=getchar();
	return f?-x:x;
}
inline void write(int x){
    if(x<0){putchar('-');x=-x;}
    if(x>9)write(x/10);
    putchar(x%10+'0');
}
inline void writeln(int x){write(x); puts("");}
inline void writepl(int x){write(x); putchar(' ');}
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
inline int randfind(int l,int r){return rnd()%(r-l+1)+l;}
//inline void init(){
//	int t=read();
//	while(t--) work();
//}
int n,m;
inline void init(){
    n=read();m=read();
}
namespace sub1{
    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;x=read();y=read();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 && !(i&(1<<(id-2)))) chkmin(f[i+(1<<(id-2))],max(f[i],a[id]-now));
        }
        printf("%lld\n",f[S]);
    }
}
namespace sub2{
    const int Maxn=70;
    vector<int> pre[Maxn];
    int father[Maxn],fa[Maxn];
    inline int getfa(int x){
        if(fa[x]==x) return x;
        return fa[x]=getfa(fa[x]);
    }
    inline void merge(int x,int y){fa[getfa(x)]=getfa(y);}
    struct node{
        int id;
        ll minn,now;
    };
    bool operator < (node A,node B){
        int flag;flag=(A.now>0)+(B.now>0);
        if(flag==1) return A.now<0;
        if(flag==2) return A.minn>B.minn;
        return A.now<B.now;
    }
    const ll inf=1e18;
    ll ans=inf;
    ll a[Maxn],b[Maxn];
    ll nowa[Maxn],nowb[Maxn];
    inline void check(){
        priority_queue<node> q;
        fr(i,1,n) fa[i]=i;
        fr(i,2,n) merge(i,father[i]);
        fr(i,2,n) if(getfa(i)!=getfa(1)) return;
        fr(i,1,n) fa[i]=i;
        nowa[1]=nowb[1]=0;
        fr(i,2,n) nowa[i]=a[i],nowb[i]=b[i];
        fr(i,2,n) q.push((node){i,a[i],b[i]});
        // fr(i,2,n) cout<<i<<' '<<father[i]<<endl;
        while(!q.empty()){
            // cerr<<"**"<<endl;
            node tmp;tmp=q.top();q.pop();
            if(tmp.id==1) continue;
            if(getfa(tmp.id)!=tmp.id || nowa[tmp.id]!=tmp.minn || nowb[tmp.id]!=tmp.now) continue;
            int Fa;Fa=getfa(father[tmp.id]);
            nowa[Fa]=max(nowa[Fa],nowa[tmp.id]-nowb[Fa]);
            nowb[Fa]+=nowb[tmp.id];merge(tmp.id,Fa);
            q.push((node){Fa,nowa[Fa],nowb[Fa]});
        }
        // fr(i,1,n) cout<<nowa[i]<<' '<<nowb[i]<<endl;
        // cout<<nowa[1]<<endl;
        ans=min(ans,nowa[1]);
    }
    inline void dfs(int x){
        if(x==(n+1)){check();return;}
        for(auto y:pre[x]){father[x]=y;dfs(x+1);}
    }
    inline void work(){
        fr(i,2,n) scanf("%lld%lld",&a[i],&b[i]);
        fr(i,1,m){int x,y;x=read();y=read();pre[y].pb(x);}
        dfs(2);
        printf("%lld\n",ans);
    }
}
inline void work(){
    if(n<=0) sub1::work();
    else sub2::work();
}
signed main(){
	// freopen("input.in","r",stdin);
	// freopen("output.out","w",stdout);
    init();work();
    // printf("\nTIME:%.3lf",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}