#include <bits/stdc++.h>

 #define ZERO(x) memset(x, 0, sizeof(x))

 using namespace std;

 using ll=long long;

 struct Edge { int v, nxt; ll c; };

 Edge w[];

 vector<int>    que;

 ll dist[], a[], b[];

 int    e[][], ww[];

 bool vis[];

 int    N, M, x, y, W = ;

 void ShortestPath(int s)

 {

     memset(dist, , sizeof(dist)); dist[s] = ;

     ZERO(vis); vis[s]=true;

     que.clear();

     que.push_back(s);

     for (int fi = ; fi < que.size(); ++ fi)

     {

         int    u = que[fi];

         for (int i = ww[u]; i; i = w[i].nxt)

         {

             int    v = w[i].v;

             if (dist[v] <= dist[u] + w[i].c) continue;

             dist[v] = dist[u] + w[i].c;

             if (vis[v]) continue;

             vis[v] = true;

             que.push_back(v);

         }

         vis[u] = false;

     }

     e[s][] = ;

     for (int i = ; i <= N; ++ i)

         if (i != s && dist[i] <= a[s]) e[s][++ e[s][]] = i;

 }

 int    main()

 {

     cin >> N >> M;

     cin >> x >> y;

     for (int i = , u, v; i <= M; ++ i)

     {

         ll    c;

         cin >> u >> v >> c;

         w[++ W].v = v; w[W].c = c; w[W].nxt = ww[u]; ww[u] = W;

         w[++ W].v = u; w[W].c = c; w[W].nxt = ww[v]; ww[v] = W;

     }

     for (int i = ; i <= N; ++ i) cin >> a[i] >> b[i];

     for (int i = ; i <= N; ++ i) ShortestPath(i);

     memset(dist, , sizeof(dist)); dist[x] = ;

     ZERO(vis); vis[x]=true;

     que.clear();

     que.push_back(x);

     for (int fi = ; fi < que.size(); ++ fi)

     {

         int    u = que[fi];

         for (int i = ; i <= e[u][]; ++ i)

         {

             int    v = e[u][i];

             if (dist[v] <= dist[u] + b[u]) continue;

             dist[v] = dist[u] + b[u];

             if (vis[v]) continue;

             vis[v] = ;

             que.push_back(v);

         }

         vis[u] = ;

     }

     if (dist[y] > (1ll << )) dist[y] = -;

     cout << dist[y] << endl;

     return ;

 }