#include <bits/stdc++.h>
using namespace std;
const int N=1010;
int a[N],A,B,vis[N];
vector<int>e[N];
int fa[N],dfn[N],low[N],id[N],tot,flag;
void Tarjan(int x){
    dfn[x]=low[x]=++tot,id[tot]=x;
    if(x==A){
        fa[B]=A;
        Tarjan(B);
    }
    // cout<<x<<"  "<<fa[x]<<"*\n";
    for(int v:e[x]){
        if(!dfn[v]){
            if(x==A)flag=1;
            fa[v]=x;
            Tarjan(v);
            low[x]=min(low[x],low[v]);
            if(low[v]>=dfn[x])flag=1;
        }else low[x]=min(low[x],dfn[v]);
    }
}
vector<int>to[N];
int in[N];
int tp[N],mp[N][N];
int main() {
    int n,m;
    scanf("%d%d%d%d",&n,&m,&A,&B);
    for(int i=1;i<=n;i++)scanf("%d",&a[i]);
    for(int i=1;i<=m;i++){
        int x,y;
        scanf("%d%d",&x,&y);
        mp[x][y]=mp[y][x]=1;
        e[x].push_back(y);
        e[y].push_back(x);
    }
    Tarjan(A);
    if(flag){printf("-1");return 0;}
    for(int i=1;i<=n;i++)in[fa[i]]++;
    queue<int>q;tot=0;tp[++tot]=A;vector<int>lf;
    for(int i=1;i<=n;i++)if(i!=A&&i!=B&&!in[i]){
        lf.push_back(i);
        q.push(i);
        vector<int>now;now.push_back(A);
        for(int x=i;;x=fa[x]){
            if(n>=200&&!mp[x][fa[x]])cout<<x<<"\n";
            if(vis[x])break;vis[x]=1;
            now.push_back(x);
            to[x]=now;
            if(x==B)break;
        }
        // cout<<"\n";
    }
    while(!q.empty()){
        int x=q.front();q.pop();if(x==A)break;
        in[fa[x]]--;if(!in[fa[x]])q.push(fa[x]);
        tp[++tot]=x;
        // cout<<x<<"";
    }
    printf("%d\n",n-1);
    for(int i=n;i>1;i--){
        int x=tp[i],sz=0;
        if(i==2)for(int v:lf)if(a[v]<a[x])x=v;
        if(i!=n)for(int v=fa[x];v!=A;v=fa[v],sz++)if(a[A]<a[v])break;
        printf("%d ",(int)to[x].size()+sz);
        int tmp=a[A];
        
        for(int i=0;i<(int)to[x].size()-1;i++)a[to[x][i]]=a[to[x][i+1]],printf("%d ",to[x][i]);
        printf("%d",x);
        if(sz){
            for(int i=1;i<=sz;i++){
                a[x]=a[fa[x]];
                x=fa[x];
                printf(" %d",x);
            }
        }
        a[x]=tmp;
        printf("\n");
    }
    return 0;
}