memset(vis,0,sizeof(vis));

queue< mypair > Q;

Q.push( mypair(start, 0) );

mypair cur, next;

int ans = -1;

vis[start]=1;

while(!Q.empty()){

cur = Q.front();

Q.pop();

if(cur.second > ans){

ans = cur.second;

fur = cur.first;

}

for(int i=0; i<sz[cur.first]; i++){

int dis = g[cur.first][i].second;

int next_pos = g[cur.first][i].first;

if(vis[next_pos]==0){

vis[next_pos]=1;

Q.push( mypair(next_pos, dis+cur.second));

}

}

}

return ans;

for(int i=1; i<=N; i++)sz[i] = g[i].size();

int fur = 0;

bfs(1,fur );

int t=-1;

int ans = bfs(fur, t);

//cout<<ans<<endl;

//bfs(start);

cout<<ans<<endl;

scanf("%d%d",&N,&M);

int a,b,c;

char d;

for(int i=0; i<N-1; i++){

a--,b--;

scanf("%d %d %d %c",&a,&b,&c,&d);

//cin>>a>>b>>c>>d;

g[a].push_back(mypair(b,c));

g[b].push_back(mypair(a,c));

}

work();

return 0;