1 #include <bits/stdc++.h> 2 #define _for(i,a,b) for(int i = (a);i < b;i ++) 3 #define _rep(i,a,b) for(int i = (a);i > b;i --) 4 #define INF 0x3f3f3f3f 5 #define MOD 1000000007 6 typedef long long ll; 7 using namespace std; 8 inline ll read() 9 { 10 ll ans = 0; 11 char ch = getchar(), last = ' '; 12 while(!isdigit(ch)) last = ch, ch = getchar(); 13 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar(); 14 if(last == '-') ans = -ans; 15 return ans; 16 } 17 inline void write(ll x) 18 { 19 if(x < 0) x = -x, putchar('-'); 20 if(x >= 10) write(x / 10); 21 putchar(x % 10 + '0'); 22 } 23 24 const int maxn = 100039; 25 int par[maxn]; 26 int high[maxn]; 27 int cnt; 28 void init(int n) 29 { 30 _for(i,1,n+1) 31 { 32 par[i] = i; 33 high[i] = 0; 34 } 35 cnt = n-1; 36 } 37 38 int find(int x) 39 { 40 return par[x] == x ? x : par[x] = find(par[x]); 41 } 42 43 void unite(int x,int y) 44 { 45 x = find(x); 46 y = find(y); 47 if(x==y) return ; 48 cnt --; 49 if(high[x]<high[y]) 50 par[x] = y; 51 else 52 { 53 par[y] = x; 54 if(high[x]==high[y]) 55 high[x] ++; 56 } 57 } 58 59 bool same(int x,int y) 60 { 61 return find(x) == find(y); 62 } 63 int N,M; 64 struct edge 65 { 66 int from; 67 int to; 68 int cost; 69 bool operator < (edge b) 70 { 71 return this->cost<b.cost; 72 } 73 }; 74 edge x[maxn]; 75 bool C(int d) 76 { 77 init(N); 78 _for(i,1,M+1) 79 if(d>=x[i].cost) 80 unite(x[i].from,x[i].to); 81 return cnt == 0; 82 } 83 int solve() 84 { 85 sort(x+1,x+M+1); 86 int lb = 0,ub = 110000; 87 while(lb < ub) 88 { 89 int mid = lb+(ub-lb)/2; 90 if(C(mid)) ub = mid; 91 else lb = mid+1; 92 } 93 return lb; 94 } 95 96 int main() 97 { 98 N = read(), M = read(); 99 int maxx; 100 _for(i,1,M+1) 101 { 102 x[i].from = read(); 103 x[i].to = read(); 104 x[i].cost = read(); 105 maxx = max(maxx,x[i].cost); 106 } 107 int rnt = solve(); 108 if(rnt>maxx) 109 printf("-1 "); 110 else 111 printf("%d ",rnt); 112 return 0; 113 }