I use BFS in the program
#include<iostream.h>
long x[2000],y[2000];
int queue[2000];
int parent[2000];
int path[2000];
int in[2000];
void main()
{

 int n;
 int i,j,tot,current,step;
 int temp;
 long need;
 cin>>n;
 for(i=1;i<=n;i++){
   in[i]=0;
   cin>>x[i]>>y[i];
 }
 cin>>need>>x[0]>>y[0];

 queue[0]=0;
 current=0;
 tot=1;
 while(current<tot){
     if(x[queue[current]]==need||y[queue[current]]==need) break;
     for(i=1;i<=n;i++){
         if(!in[i]){
             if((x[i]==x[queue[current]])||(x[i]==y[queue
[current]])||(y[i]==x[queue[current]])||(y[i]==y[queue[current]])){
               queue[tot]=i;
               parent[i]=queue[current];
               in[i]=1;
               tot++;
             }
         }
     }
     current++;
 }

 if(x[queue[current]]==need||y[queue[current]]==need){
     step=0;
     temp=queue[current];
     while(1){
      if(temp==0) break;
      step++;
      path[step]=temp;
      temp=parent[temp];
     }
     cout<<step<<endl;
     for(j=step;j>=1;j--){
      cout<<path[j]<<endl;
     }
 }else{
  cout<<"IMPOSSIBLE"<<endl;
 }
}