#include<bits/stdc++.h>
#define int long long
#define pii pair<int,int>
using namespace std;
int T,n,m,x[2005],y[2005],z[2005],dis[2005],vis[2005],ps,ans=1e18;
struct node{int to,w,id;};
vector<node> v[2005];
void dij(int s){
    priority_queue<pii,vector<pii>,greater<pii>> pq;
    memset(dis,0x3f,sizeof(dis)),memset(vis,0,sizeof(vis));
    dis[s]=0,pq.push({0,s});
    while(pq.size()){
        int x=pq.top().second;pq.pop();
        if(vis[x])continue;vis[x]=1;
        for(auto i:v[x]){
            if(i.id==ps)continue;
            if(dis[i.to]>dis[x]+i.w){
                dis[i.to]=dis[x]+i.w;
                pq.push({dis[i.to],i.to});
            }
        }
    }
}
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    cin>>T>>n>>m;
    for(int i=1;i<=m;i++)cin>>x[i]>>y[i]>>z[i],v[x[i]].push_back((node){y[i],z[i],i}),((!T)?v[y[i]].push_back((node){x[i],z[i],i}):void());
    for(ps=1;ps<=m;ps++)dij(y[ps]),ans=min(ans,dis[x[ps]]+z[ps]);
    if(ans>1e12)cout<<-1;
    else cout<<ans;
    return 0;
}