vector<ll> e[2000];
ll c[2000],s[2000];

void f(ll i,ll*d){
	ll g[2001];
	rep(k,2001){
		if(k-s[i]<0){
			//g[k]=c[i];
			g[k]=ll_inf;
		}else{
			g[k]=c[i]+d[k-s[i]];
		}
	}
	for(ll j:e[i]){
		f(j,g);
	}
	rep(k,2001){
		d[k]<?=g[k];
	}
}

{
	ll@n,@x;
	rep(i,1,n){
		ll@p--;
		e[p].push_back(i);
	}
	c[0]=0;
	s[0]=0;
	rep(i,1,n){
		rd(c[i],s[i]);
	}
	ll d[2001];
	d[0]=0;
	rep(i,1,2001){
		d[i]=ll_inf;
	}
	f(0,d);
	//wt(d[x]);
	wt(min[i,x,2000](d[i]));
}