// #include "atcoder/convolution"
#include "atcoder/dsu"
#include "atcoder/fenwicktree"
#include "atcoder/lazysegtree"
#include "atcoder/math"
#include "atcoder/maxflow"
#include "atcoder/mincostflow"
#include "atcoder/modint"
#include "atcoder/scc"
#include "atcoder/segtree"
#include "atcoder/string"
#include "atcoder/twosat"
using namespace atcoder;
#include <bits/stdc++.h>
using namespace std;
// #include <boost/multiprecision/cpp_int.hpp>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for (int i = (int)(a); i < (int)(b); i++)
#define all(v) v.begin(),v.end()
#define inc(x,l,r) ((l)<=(x)&&(x)<(r)) 
#define Unique(x) sort(all(x)), x.erase(unique(all(x)), x.end())
#define pcnt __builtin_popcountll
typedef long long ll;
#define int ll
using ld = long double;
using vi = vector<int>;
using vs = vector<string>;
using P = pair<int,int>;
using vp = vector<P>;
// using Bint = boost::multiprecision::cpp_int;
template<typename T1,typename T2> bool chmax(T1 &a, const T2 b) {if (a < b) {a = b; return true;} else return false; }
template<typename T1,typename T2> bool chmin(T1 &a, const T2 b) {if (a > b) {a = b; return true;} else return false; }
template<typename T> using priority_queue_greater = priority_queue<T, vector<T>, greater<T>>;
template<typename T> istream &operator>>(istream& is,vector<T> &v){for(T &in:v)is>>in;return is;}
template<typename T1,typename T2> ostream &operator<< (ostream &os, const pair<T1,T2> &p){os << p.first <<" "<<p.second;return os;}
ostream &operator<< (ostream &os, const modint1000000007 &m){os << m.val();return os;}
istream &operator>> (istream &is, modint1000000007 &m){ll in;is>>in;m=in;return is;}
ostream &operator<< (ostream &os, const modint998244353 &m){os << m.val();return os;}
istream &operator>> (istream &is, modint998244353 &m){ll in;is>>in;m=in;return is;}
template<class... T> void input(T&... a){(cin>> ... >> a);}
#ifdef LOCAL
template<typename T> ostream &operator<<(ostream &os,const vector<T> &v){os<<"\x1b[32m";rep(i,v.size())os<<v[i]<<(i+1!=v.size()?" ":"");os<<"\x1b[0m";return os;}
template<class T> void print(T& a){cout << "\x1b[32m"<< a<< '\n' << "\x1b[0m";}
template<class T,class... Ts> void print(const T&a, const Ts&... b){cout << "\x1b[32m" << a;(cout<<...<<(cout<<' ',b));cout<<'\n' << "\x1b[0m";}
#else
template<typename T> ostream &operator<<(ostream &os,const vector<T> &v){rep(i,v.size())os<<v[i]<<(i+1!=v.size()?" ":"");return os;}
template<class T> void print(T& a){cout << a<< '\n';}
template<class T,class... Ts> void print(const T&a, const Ts&... b){cout << a;(cout<<...<<(cout<<' ',b));cout<<'\n';}
#endif
#define VI(v,n) vi v(n); input(v)
#define INT(...) int __VA_ARGS__; input(__VA_ARGS__)
#define STR(...) string __VA_ARGS__; input(__VA_ARGS__)
#define CHAR(...) char __VA_ARGS__; input(__VA_ARGS__)
int sign(ll x){return x>0?1:x<0?-1:0;}
ll ceil(ll x,ll y){assert(y!=0);if(sign(x)==sign(y))return (x+y-1)/y;return -((-x/y));}
ll floor(ll x,ll y){assert(y!=0);if(sign(x)==sign(y))return x/y;if(y<0)x*=-1,y*=-1;return x/y-(x%y<0);}
ll abs(ll x,ll y){return abs(x-y);}
ll bit(int n){return 1ll<<n;}
bool ins(string s,string t){return s.find(t)!=string::npos;}
P operator+ (const P &p, const P &q){ return P{p.first+q.first,p.second+q.second};}
P operator- (const P &p, const P &q){ return P{p.first-q.first,p.second-q.second};}
int yesno(bool ok,string y="Yes",string n="No"){ cout<<(ok?y:n)<<endl;return 0;}
int YESNO(bool ok,string y="YES",string n="NO"){ cout<<(ok?y:n)<<endl;return 0;}
int di[]={-1,0,1,0,-1,-1,1,1};
int dj[]={0,1,0,-1,-1,1,-1,1};
const ll INF = 8e18;
//using mint = modint1000000007;
//using mint = modint998244353;
//mint stom(const string &s,int b=10){mint res = 0;for(auto c:s)res *= b,res += c-'0';return res;}
template<typename T=int>struct edge{int to;T cost;int idx;};
template<typename T=int>class Graph{
public:
    int n;
    bool weighted,directed;
    vector<pair<int,edge<T>>> edges;
    vector<vector<edge<T>>> E;

    Graph(int n,bool weighted=false,bool directed=false):n(n),weighted(weighted),directed(directed),E(n){}
    void add_edge(int u,int v,T w=1){
        int idx = edges.size();
        E[u].push_back({v,w,idx});
        if(!directed)E[v].push_back({u,w,idx});
        edges.push_back({u,{v,w,idx}});
    }
    void read_edge(int m,int index=1){
        rep(i,m){
            int u,v;
            cin>>u>>v;
            u-=index,v-=index;
            if(weighted){
                T w;cin>>w;
                add_edge(u,v,w);
            }
            else add_edge(u,v);
        }
    }
    inline const vector<edge<T>> &operator[](int u) const { return E[u]; }
    inline vector<edge<T>> &operator[](int u) { return E[u]; }
    pair<int,edge<T>> get_edge(int i){return edges[i];}
};
template<typename T>
class dijkstra{
public:
    dijkstra(const Graph<T> &G,int s=0,set<int> ban={}):n(G.n),s(s),d(G.n,INF),edge_idx(G.n,-1),pre(G.n,-1){
        d[s] = 0;
        if(G.weighted){
            priority_queue_greater<pair<T,int>> pq;pq.emplace(0,s);
            while(pq.size()){
                auto [td,u] = pq.top();pq.pop();
                if(d[u]<td)continue;
                for(const auto &e:G.E[u]){
                if(ban.size()&&ban.count(e.idx))continue;
                    if(chmin(d[e.to],d[u]+e.cost)){
                        pq.emplace(d[e.to],e.to);
                        edge_idx[e.to]=e.idx;
                        pre[e.to] = u;
                    }
                }
            }
        }
        else{//bfs
            queue<int> q;q.push(s);
            while(q.size()){
                auto u = q.front();q.pop();
                for(const auto &e:G.E[u]){
                if(ban.size()&&ban.count(e.idx))continue;
                    if(chmin(d[e.to],d[u]+e.cost)){
                        q.push(e.to);
                        edge_idx[e.to]=e.idx;
                        pre[e.to] = u;
                    }
                }
            }
        }
    }
    T dist(int u){return d[u];}
    const vector<T> &dist(){return d;}

private:
    int n,s;
    vector<T> d;
    vector<int> edge_idx,pre;
};


signed main() {
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    INT(t);
    INT(n,m);
    Graph G(n,1,t);
    G.read_edge(m);
    int ans = INF;
    rep(i,m){
        auto [u,e] = G.get_edge(i);
        auto [v,w,id] = e;
        dijkstra d(G,v,{id});
        auto dist = d.dist(u);
        chmin(ans,dist+w);
    }
    if(ans==INF)ans=-1;
    print(ans);
    return 0;
}