#include <bits/stdc++.h>

//{{{ graph.hpp
#ifndef INCLUDE_GRAPH_HPP
#define INCLUDE_GRAPH_HPP
#include <vector>
namespace orislib {
struct Edge {
  typedef int weight_t;
  int from, to;
  weight_t w;
  Edge(int from, int to, weight_t w) : from(from), to(to), w(w) {}
  bool operator<(const Edge& e) const {
    return w != e.w ? w > e.w : from != e.from ? from < e.from : to < e.to;
  }
  static const weight_t INF;
};
const int Edge::INF=INT_MAX;
typedef std::vector<Edge> Edges;
typedef std::vector<Edges> Graph;
}
#endif
//}}}

using namespace std;
using namespace orislib;

typedef long long ll;
typedef long double ld;
typedef tuple<int, int> duo;
const int dx[] = {0, 0, 1, -1, 1, 1, -1, -1};
const int dy[] = {1, -1, 0, 0, 1, -1, 1, -1};
const int Mod = 1000000000 + 0;
//{{{ templates
#define TT_ template<typename T>inline
#define TTF_ template<typename T,typename F>inline
TT_ T sq(T x){return x*x;}
TT_ T In(){T x;cin>>x;return x;}
TT_ void Out(T&x){cout<<x;}
TT_ void sort(T&v){sort(begin(v),end(v));}
TT_ void revs(T&v){reverse(begin(v),end(v));}
TT_ void uniq(T&v){sort(v);v.erase(unique(begin(v),end(v)),end(v));}
TT_ int ubnd(T&v,typename T::value_type x){return upper_bound(begin(v),end(v),x)-begin(v);}
TT_ int lbnd(T&v,typename T::value_type x){return lower_bound(begin(v),end(v),x)-begin(v);}
TTF_ void inpt(T&v,int n,F f){for(v.reserve(n);n--;v.emplace_back(f()));}
TTF_ void show(T&v,F f,string d=" ",string e="\n"){int i=0;for(auto&x:v)i++&&(cout<<d),f(x);cout<<e;}
TT_ typename T::iterator minel(T&v){return min_element(begin(v),end(v));}
TT_ typename T::iterator maxel(T&v){return max_element(begin(v),end(v));}

inline void fast_io(){ios_base::sync_with_stdio(0);cin.tie(0);}
inline int in(){int x;scanf("%d",&x);return x;}
inline ll pow_mod(ll a,ll k,ll m){ll r=1;for(;k>0;a=a*a%m,k>>=1)if(k&1)r=r*a%m;return r;}
inline ll mod_inv(ll a,ll p){return pow_mod(a,p-2,p);}
//}}} priority_queue queue deque front stringstream max_element min_element insert count make_tuple

//{{{ void dijkstra(g, s, &dist, &prev)
void dijkstra(const Graph& g, int s, vector<Edge::weight_t>& dist, vector<int>& prev)
{
  const int V = g.size();
  prev.assign(V, -1);
  dist.assign(V, Edge::INF);
  dist[s] = 0;
  priority_queue<Edge> pq;
  for (pq.push(Edge(-2, s, 0)); !pq.empty();){
    Edge c = pq.top();
    pq.pop();
    if (prev[c.to] != -1) continue;
    prev[c.to] = c.from;
    for (const auto& e : g[c.to]){
      if (dist[e.to] > e.w + c.w){
        dist[e.to] = e.w + c.w;
        pq.push(Edge(e.from, e.to, e.w + c.w));
      }
    }
  }
}
//}}}

struct Solver {
  const int N, K;
  Graph G, pG;
  vector<int> C, R;
  Solver(int N, int K) : N(N), K(K), G(N), pG(N), C(N), R(N) {}
  void read(){
    for (int i = 0; i < N; i++){
      C[i] = in(), R[i] = in();
    }
    for (int i = 0; i < K; i++){
      int f, t;
      f = in() - 1, t = in() - 1;
      pG[f].emplace_back(f, t, 1);
      pG[t].emplace_back(t, f, 1);
    }
  }
  void build(){
    for (int i = 0; i < N; i++){
      vector<int> dist, prev;
      dijkstra(pG, i, dist, prev);
      for (int j = 0; j < N; j++){
        if (i == j) continue;
        if (R[i] < dist[j]) continue;
        G[i].emplace_back(i, j, C[i]);
      }
    }
  }
  void solve(){
    vector<int> dist, prev;
    dijkstra(G, 0, dist, prev);
    printf("%d\n", dist[N - 1]);
  }
};

int main()
{
  int N, K;
  N = in(), K = in();
  Solver sol(N, K);
  sol.read();
  sol.build();
  sol.solve();
  return 0;
}

Measured memory_bytes: 182976