#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) chkmin(f[i+(1<<(id-2))],max(f[i],a[id]-now));
        }
        printf("%lld\n",f[S]);
    }
}
inline void work(){
    if(n<=26) 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;
}