1 //OJ 2077 2 //by Cydiater 3 //2016.9.23 4 #include <iostream> 5 #include <cstdio> 6 #include <cstring> 7 #include <string> 8 #include <algorithm> 9 #include <queue>10 #include <map>11 #include <ctime>12 #include <cmath>13 #include <iomanip>14 #include <cstdlib>15 using namespace std;16 #define ll long long17 #define up(i,j,n)        for(int i=j;i<=n;i++)18 #define down(i,j,n)        for(int i=j;i>=n;i--)19 const int MAXN=1e6+5;20 const int oo=0x3f3f3f3f;21 inline int read(){22     char ch=getchar();int x=0,f=1;23     while(ch>‘9‘||ch<‘0‘){if(ch==‘-‘)f=-1;ch=getchar();}24     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}25     return x*f;26 }27 int LINK[MAXN],len=0,sum,max_siz[MAXN],root,siz[MAXN],dis[MAXN],head,tail,q[MAXN],cnt[3],ans=0;28 bool vis[MAXN];29 struct edge{30     int y,next,v;31 }e[MAXN<<1];32 int N;33 namespace solution{34     inline void insert(int x,int y,int v){e[++len].next=LINK[x];LINK[x]=len;e[len].y=y;e[len].v=v;}35     inline int gcd(int a,int b){return b==0?a:gcd(b,a%b);}36     void init(){37         N=read();38         memset(vis,0,sizeof(vis));39         up(i,2,N){40             int x=read(),y=read(),v=read();41             insert(x,y,v);42             insert(y,x,v);43         }44     }45     void make_root(int node,int fa){46         max_siz[node]=0;siz[node]=1;47         for(int i=LINK[node];i;i=e[i].next)if(!vis[e[i].y]&&e[i].y!=fa){48             make_root(e[i].y,node);49             siz[node]+=siz[e[i].y];50             max_siz[node]=max(max_siz[node],siz[e[i].y]);51         }52         max_siz[node]=max(max_siz[node],sum-max_siz[node]);53         if(max_siz[node]<max_siz[root])root=node;54     }55     void get_deep(int node,int fa){56         q[++tail]=dis[node];57         for(int i=LINK[node];i;i=e[i].next)if(e[i].y!=fa&&!vis[e[i].y]){58             dis[e[i].y]=dis[node]+e[i].v;59             get_deep(e[i].y,node);60         }61     }62     int col(int node,int dist){63         dis[node]=dist;head=1;tail=0;64         get_deep(node,0);65         cnt[0]=cnt[1]=cnt[2]=0;66         up(i,head,tail)cnt[q[i]%3]++;67         return cnt[0]*cnt[0]+2*cnt[1]*cnt[2];68     }69     void work(int node){70         ans+=col(node,0);71         vis[node]=1;72         for(int i=LINK[node];i;i=e[i].next)if(!vis[e[i].y]){73             ans-=col(e[i].y,e[i].v);74             root=0;75             make_root(e[i].y,node);76             work(root);77         }78     }79     void slove(){80         sum=N;max_siz[0]=oo;root=0;81         make_root(1,0);82         work(root);83     }84     void output(){85         int d=gcd(ans,N*N);86         printf("%d/%d\n",ans/d,N*N/d);87     }88 }89 int main(){90     //freopen("input.in","r",stdin);91     using namespace solution;92     init();93     slove();94     output();95     return 0;96 }