1 program pku1985(input,output); 2 type 3    node    = ^link; 4    link    = record  5          goal,w : longint; 6          next   : node; 7       end;         8 var 9    l   : array[0..50000] of node;10    d   : array[0..50000] of longint;11    v   : array[0..50000] of boolean;12    n,m : longint;13 procedure add(xx,yy,ww :longint );14 var15    tt : node;16 begin17    new(tt);18    tt^.next:=l[xx];19    tt^.goal:=yy;20    tt^.w:=ww;21    l[xx]:=tt;22 end; { add }23 procedure init;24 var25    i,xxx,yyy,www : longint;26 begin27    readln(n,m);28    for i:=1 to n do29       l[i]:=nil;30    for i:=1 to m do31    begin32       readln(xxx,yyy,www);33       add(xxx,yyy,www);34       add(yyy,xxx,www);35    end;36 end; { init }37 procedure dfs(now,dist : longint );38 var39    t : node;40 begin41    d[now]:=dist;42    t:=l[now];43    while t<>nil do44    begin45       if not v[t^.goal] then46       begin47      v[t^.goal]:=true;48      dfs(t^.goal,dist+t^.w);49       end;50       t:=t^.next;51    end;52 end; { dfs }53 procedure main;54 var55    i,maxn,maxl : longint;56 begin57    fillchar(d,sizeof(d),0);58    fillchar(v,sizeof(v),false);59    v[1]:=true;60    dfs(1,0);61    maxl:=0;62    for i:=1 to n do63       if d[i]>maxl then64       begin65      maxl:=d[i];66      maxn:=i;67       end;68    fillchar(d,sizeof(d),0);69    fillchar(v,sizeof(v),false);70    v[maxn]:=true;71    dfs(maxn,0);72    maxl:=0;73    for i:=1 to n do74       if d[i]>maxl then75      maxl:=d[i];76    writeln(maxl);77 end; { main }78 begin79    init;80    main;81 end.