#include<bits/stdc++.h>
#define int long long
using namespace std;
int a[105],b[105],n,m;
void cmin(int &x,int y){x=(x<y?x:y);}
const int inf=0x3f3f3f3f3f3f3f3f;
namespace Sub1
{
	int dp[20000005],e[105],u,v;
	void main()
	{
		for(int i=1;i<=m;i++)
		{
			cin>>u>>v;u--;v--;
			e[u]|=(1<<v);
		}
		for(int s=0;s<(1<<n);s++)dp[s]=inf;
		dp[1]=a[1];
		for(int s=1;s<(1<<n);s++)
		{
			int t=0;
			for(int i=0;i<n;i++)if(s&(1<<i))t|=e[i];
			int now=dp[s];
			for(int i=0;i<n;i++)if(s&(1<<i))now-=a[i+1],now+=b[i+1];
			t=(t|s)^s;
			for(int i=0;i<n;i++)
			{
				if(!(t&(1<<i)))continue;
				cmin(dp[s|(1<<i)],dp[s]+max(0ll,a[i+1]-now));
			}
		}
		cout<<dp[(1<<n)-1];
	}
}
namespace Sub2
{
	struct node{int u,c,w;}val[105];
	int ans=inf,vis[105],fa[105],u,v;vector<int>g[105];
	bool operator <(node x,node y)
	{
		if(max(x.c,y.c-x.w)!=max(y.c,x.c-y.w))return max(x.c,y.c-x.w)<max(y.c,x.c-y.w);
		return x.u<y.u;
	}
	node operator +(node x,node y)
	{
		return node{x.u,max(x.c,y.c-x.w),x.w+y.w};
	}
	void solve()
	{
		for(int i=1;i<=n;i++)vis[i]=0;
		set<node>s;
		//max(c[u],c[v]-w[u])<max(c[v],c[u]-w[v])
		for(int i=1;i<=n;i++)s.insert(val[i]=node{i,a[i],b[i]-a[i]});
		node res={0,0,0};
		while(s.size())
		{
			node now=*s.begin();s.erase(s.find(now));
			int x=fa[now.u];
			while(x&&vis[x])x=fa[x];
			if(x==0)res=res+now;
			else 
			{
				s.erase(s.find(val[x]));
				val[x]=val[x]+now;
				s.insert(val[x]); 
			}
			vis[now.u]=1;
		}
		ans=min(ans,res.c);
	}
	void search(int x)
	{
		if(x==n+1){solve();return;}
		for(int i=0;i<g[x].size();i++)
		{
			fa[x]=g[x][i];
			search(x+1);
		}
	}
	void main()
	{
		for(int i=1;i<=m;i++)
		{
			cin>>u>>v;
			g[v].emplace_back(u);
		}
		search(2);
		cout<<ans;
	}
}
signed main()
{
	cin.tie(0)->sync_with_stdio(0);
	cin>>n>>m;
	for(int i=2;i<=n;i++)cin>>a[i]>>b[i];
	if(n<=25)Sub1::main();
	else Sub2::main();
	return 0;
}