#include<bits/stdc++.h>
using namespace std;
void *wmem;
inline void rd(int &x){
  int k, m=0;
  x=0;
  for(;;){
    k = getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
inline void wt_L(char a){
  putchar_unlocked(a);
}
inline void wt_L(int x){
  char f[10];
  int m=0, s=0;
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    putchar_unlocked('-');
  }
  while(s--){
    putchar_unlocked(f[s]+'0');
  }
}
struct graph{
  int N, **edge, *es;
  void setEdge(int N__, int M, int A[], int B[], void **mem = &wmem){
    int i;
    N = N__;
    es = (int*)(*mem);
    edge = (int**)(es+N);
    edge[0] = (int*)(edge+N);
    for(i=0;i<N;i++){
      es[i] = 0;
    }
    for(i=0;i<M;i++){
      es[A[i]]++;
      es[B[i]]++;
    }
    for(i=1;i<N;i++){
      edge[i] = edge[i-1] + es[i-1];
    }
    (*mem) = edge[N-1] + es[N-1];
    for(i=0;i<N;i++){
      es[i] = 0;
    }
    for(i=0;i<M;i++){
      edge[A[i]][es[A[i]]++] = B[i];
      edge[B[i]][es[B[i]]++] = A[i];
    }
  }
  void setDirectEdge(int N__, int M, int A[], int B[], void **mem = &wmem){
    int i;
    N = N__;
    es = (int*)(*mem);
    edge = (int**)(es+N);
    edge[0] = (int*)(edge+N);
    for(i=0;i<N;i++){
      es[i] = 0;
    }
    for(i=0;i<M;i++){
      es[A[i]]++;
    }
    for(i=1;i<N;i++){
      edge[i] = edge[i-1] + es[i-1];
    }
    (*mem) = edge[N-1] + es[N-1];
    for(i=0;i<N;i++){
      es[i] = 0;
    }
    for(i=0;i<M;i++){
      edge[A[i]][es[A[i]]++] = B[i];
    }
  }
  graph reverse(void **mem = &wmem){
    graph g;
    int i, j, k;
    g.N = N;
    g.es = (int*)(*mem);
    g.edge = (int**)(g.es + N);
    g.edge[0] = (int*)(g.edge + N);
    for(i=0;i<N;i++){
      g.es[i] = 0;
    }
    for(i=0;i<N;i++){
      for(j=0;j<es[i];j++){
        g.es[edge[i][j]]++;
      }
    }
    for(i=1;i<N;i++){
      g.edge[i] = g.edge[i-1] + g.es[i-1];
    }
    *mem = g.edge[N-1] + g.es[N-1];
    for(i=0;i<N;i++){
      g.es[i] = 0;
    }
    for(i=0;i<N;i++){
      for(j=0;j<es[i];j++){
        k = edge[i][j];
        g.edge[k][g.es[k]++] = i;
      }
    }
    return g;
  }
  graph reduce(int tn, int ind[], int self_e = 0, int dep_e = 0, void **mem = &wmem){
    graph g;
    int M=0, i, j, k, x, y;
    pair<int,int> *A;
    for(i=0;i<N;i++){
      M += es[i];
    }
    A = (pair<int,int>*)((int*)((int**)(*mem) + tn) + tn + M);
    M = 0;
    for(i=0;i<N;i++){
      x = ind[i];
      if(x < 0){
        continue;
      }
      for(j=0;j<es[i];j++){
        y = ind[edge[i][j]];
        if(y < 0){
          continue;
        }
        if(self_e==0 && x==y){
          continue;
        }
        A[M++] = make_pair(x, y);
      }
    }
    if(dep_e==0){
      sort(A, A+M);
      k = 0;
      for(i=0;i<M;i++){
        if(k && A[k-1]==A[i]){
          continue;
        }
        A[k++] = A[i];
      }
      M = k;
    }
    g.N = tn;
    g.es = (int*)(*mem);
    g.edge = (int**)(g.es + tn);
    g.edge[0] = (int*)(g.edge + tn);
    for(i=0;i<tn;i++){
      g.es[i] = 0;
    }
    for(i=0;i<M;i++){
      g.es[A[i].first]++;
    }
    for(i=1;i<tn;i++){
      g.edge[i] = g.edge[i-1] + g.es[i-1];
    }
    *mem = g.edge[tn-1] + g.es[tn-1];
    for(i=0;i<tn;i++){
      g.es[i] = 0;
    }
    for(i=0;i<M;i++){
      j = A[i].first;
      k = A[i].second;
      g.edge[j][g.es[j]++] = k;
    }
    return g;
  }
  void getDist(int root, int res[], void *mem = wmem){
    int i, j, k, *q, s, z;
    q=(int*)mem;
    for(i=0;i<N;i++){
      res[i]=-1;
    }
    res[root]=0;
    s=0;
    z=1;
    q[0]=root;
    while(z){
      i=q[s++];
      z--;
      for(j=0;j<es[i];j++){
        k=edge[i][j];
        if(res[k]>=0){
          continue;
        }
        res[k]=res[i]+1;
        q[s+z++]=k;
      }
    }
  }
  inline int sccDFS(int num[], int st, int mx){
    int i, j;
    num[st]=-2;
    for(i=0;i<es[st];i++){
      j=edge[st][i];
      if(num[j]==-1){
        mx=sccDFS(num,j,mx);
      }
    }
    num[st]=mx;
    return mx+1;
  }
  int scc(int res[], void *mem = wmem){
    graph r;
    int i, j, k, *nrv, *num, ret=0, *st, st_size;
    r = reverse(&mem);
    st = (int*)mem;
    num = st+N;
    nrv = num + N;
    for(i=0;i<N;i++){
      res[i] = num[i] = -1;
    }
    k = 0;
    for(i=0;i<N;i++){
      if(num[i]==-1){
        k = sccDFS(num,i,k);
      }
    }
    for(i=0;i<N;i++){
      nrv[num[i]] = i;
    }
    for(k=N-1;k>=0;k--){
      i=nrv[k];
      if(res[i]>=0){
        continue;
      }
      res[i]=ret;
      st_size=0;
      st[st_size++]=i;
      while(st_size){
        i=st[--st_size];
        for(j=0;j<r.es[i];j++){
          if(res[r.edge[i][j]]==-1){
            res[r.edge[i][j]]=ret;
            st[st_size++]=r.edge[i][j];
          }
        }
      }
      ret++;
    }
    return ret;
  }
  inline void bccDFS(int v, int u, int *res, int *rt, int &rts, int *S, int &Ss, int *inS, int *num, int &tm){
    int i, k;
    num[v] = ++tm;
    S[Ss++] = v;
    inS[v] = 1;
    rt[rts++] = v;
    for(i=0;i<es[v];i++){
      int w=edge[v][i];
      if(!num[w]){
        bccDFS(w, v, res, rt, rts, S, Ss, inS, num, tm);
      }
      else if(u != w && inS[w]){
        while(num[rt[rts-1]] > num[w]){
          rts--;
        }
      }
    }
    if(v == rt[rts-1]){
      k = S[Ss-1];
      for(;;){
        int w=S[--Ss];
        inS[w] = 0;
        res[w] = k;
        if(v==w){
          break;
        }
      }
      rts--;
    }
  }
  int bcc(int res[], void *mem=wmem){
    int *S, Ss=0, i, *inS, k, *num, *rt, rts=0, tm=0;
    pair<int,int> *arr;
    num = (int*)mem;
    rt = num + N;
    S = rt + N;
    inS = S + N;
    memset(num, 0, sizeof(int)*N);
    memset(inS, 0, sizeof(int)*N);
    for(i=0;i<N;i++){
      if(!num[i]){
        bccDFS(i, N, res, rt, rts, S, Ss, inS, num, tm);
      }
    }
    arr = (pair<int,int>*)mem;
    for(i=0;i<N;i++){
      arr[i].first = res[i];
      arr[i].second = i;
    }
    sort(arr, arr+N);
    k = 0;
    for(i=0;i<N;i++){
      if(i && arr[i].first != arr[i-1].first){
        k++;
      }
      res[arr[i].second] = k;
    }
    return k+1;
  }
}
;
char memarr[96000000];
int N;
int M;
int U[300000];
int V[300000];
int S;
int T;
int dist[300000];
int main(){
  graph g;
  int i, j, k;
  wmem = memarr;
  rd(N);
  rd(M);
  {
    int Lj4PdHRW;
    for(Lj4PdHRW=0;Lj4PdHRW<M;Lj4PdHRW++){
      rd(U[Lj4PdHRW]);
      rd(V[Lj4PdHRW]);
    }
  }
  rd(S);
  rd(T);
  S--;
  T--;
  for(i=0;i<M;i++){
    U[i]--;
    V[i]--;
    U[i+M] = U[i] + N;
    V[i+M] = V[i] + 2*N;
    U[i+2*M] = U[i] + 2*N;
    V[i+2*M] = V[i];
    V[i] += N;
  }
  g.setDirectEdge(3*N, 3*M, U, V);
  g.getDist(S, dist);
  if(dist[T]==-1){
    wt_L(-1);
    wt_L('\n');
  }
  else{
    wt_L(dist[T]/3);
    wt_L('\n');
  }
  return 0;
}
// cLay varsion 20190626-1

// --- original code ---
// int N, M;
// int U[3d5], V[3d5], S, T;
// int dist[3d5];
// {
//   int i, j, k;
//   graph g;
//   rd(N,M,(U,V)(M),S,T);
// 
//   S--; T--;
//   rep(i,M){
//     U[i]--; V[i]--;
//     U[i+M] = U[i] + N;
//     V[i+M] = V[i] + 2N;
//     U[i+2M] = U[i] + 2N;
//     V[i+2M] = V[i];
//     V[i] += N; 
//   }
// 
//   g.setDirectEdge(3N, 3M, U, V);
//   g.getDist(S, dist);
//   wt( if[dist[T]==-1, -1, dist[T]/3] );
// }


Measured memory_bytes: 10496