1 #include <set>
 2 #include <cstdio>
 3 #include <algorithm>
 4
 5 const int MAXE=2000010;
 6 const int MAXV=1000010;
 7
 8 struct Edge{
 9     int from;
10     int to;
11     int dis;
12     Edge* next;
13 };
14 Edge E[MAXE];
15 Edge* head[MAXV];
16 Edge* top=E;
17
18 int n;
19 int m;
20 int lg1;
21 int lg2;
22 int dis[MAXV];
23
24 void Initialize();
25 std::pair<int,int> DFS(int,int,int);
26 void DFSA(int,int,int);
27 void Insert(int,int,int);
28 int Sweep();
29
30 int main(){
31     Initialize();
32     lg1=DFS(1,0,0).second;
33     lg2=DFS(lg1,0,0).second;
34     DFSA(lg1,0,0);
35     DFSA(lg2,0,0);
36     printf("%d\n",Sweep());
37     // printf("%d %d\n",lg1,lg2);
38     return 0;
39 }
40
41 std::pair<int,int> DFS(int root,int prt,int dis){
42     std::pair<int,int> ans(dis,root);
43     for(Edge* i=head[root];i!=NULL;i=i->next){
44         if(i->to==prt)
45             continue;
46         ans=std::max(ans,DFS(i->to,root,dis+i->dis));
47     }
48     return ans;
49 }
50
51 void DFSA(int root,int prt,int dis){
52     ::dis[root]=std::max(::dis[root],dis);
53     for(Edge* i=head[root];i!=NULL;i=i->next){
54         if(i->to==prt)
55             continue;
56         DFSA(i->to,root,dis+i->dis);
57     }
58 }
59
60 int Sweep(){
61     int l=1,r=1,ans=0;
62     // std::priority_queue<int,std::vector<int>,std::less<int>> qmax;
63     // std::priority_queue<int,std::vector<int>,std::greater<int>> qmin;
64     std::multiset<int> s;
65     while(r<=n){
66         // printf("%d\n",r);
67         s.insert(dis[r]);
68         while(*(--s.end())-*s.begin()>m){
69             s.erase(s.find(dis[l]));
70             ++l;
71         }
72         ans=std::max(ans,int(s.size()));
73         ++r;
74     }
75     return ans;
76 }
77
78 void Initialize(){
79     int a,b;
80     scanf("%d%d",&n,&m);
81     for(int i=2;i<=n;i++){
82         scanf("%d%d",&a,&b);
83         Insert(a,i,b);
84         Insert(i,a,b);
85     }
86 }
87
88 inline void Insert(int from,int to,int dis){
89     top->to=to;
90     top->dis=dis;
91     top->from=from;
92     top->next=head[from];
93     head[from]=top;
94     top++;
95 }