#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

//template
#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
typedef long long int ll;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
//end

typedef pair<ll,ll> P;
typedef pair<P,ll> T;
int t,n,m;
set<P> g[2010];
ll dijk(int u,int v){
   ll dist[2010];
   rep(i,0,n)dist[i]=INF;
   dist[u]=0;
   priority_queue<P,vector<P>,greater<P>> pq;
   pq.push({0,u});
   while(!pq.empty()){
      auto [d,x]=pq.top(); pq.pop();
      if(dist[x]<d)continue;
      if(x==v)return d;
      for(auto [to,add]:g[x]){
         if(chmin(dist[to],d+add)){
            pq.push({dist[to],to});
         }
      }
   }
   return INF;
}

int main(){
   cin>>t>>n>>m;
   vector<T> es;
   rep(i,0,m){
      int u,v,w; cin>>u>>v>>w;
      es.push_back({{u,v},w});
      g[u].insert({v,w});
      if(!t)g[v].insert({u,w});
   }
   ll res=INF;
   for(auto [p,w]:es){
      auto [u,v]=p;
      g[u].erase({v,w});
      if(!t)g[v].erase({u,w});
      chmin(res,dijk(v,u)+w);
      g[u].insert({v,w});
      if(!t)g[v].insert({u,w});
   }
   if(res==INF)puts("-1");
   else cout<<res<<endl;
   return 0;
}