Great Escape

/*
 Created By: Malvika Joshi
 Problem: GREATESC
 Link: http://opc.iarcs.org.in/index.php/problems/GREATESC
*/

#include <stdio.h>
#include <limits.h>

#define INF -1
int n;
int D[4000];
int Q[4000];
int A[4000][4000];

void BFS(int b){
    int H = 0;
    int T = -1;
    int j,k;
    D[b] = 0;

    Q[T+1] = b;
    T = T+1;

    while(T>=H){
        j = Q[H];

        for (k = 0;k < n; k++){
            if(A[j][k] == 1 && D[k] == INF){
                D[k] = D[j]+1;
                Q[T+1] = k;
                T = T+1;
            }
        }

        H = H+1;
    }
}

int main(){
    int m;
    scanf("%d%d",&n,&m);
    int i,j;
    int a,b,s,t;

    for(i = 0;i < n; i++){
        D[i] = INF;
    }

    for(i = 0;i < n; i++){
        for(j = 0;j < n; j++){
            A[i][j] = 0;
        }
    }

    for(i = 0;i < m; i++){
        scanf("%d%d",&a,&b);
        A[a-1][b-1] = 1;
        A[b-1][a-1] = 1;
    }


    scanf("%d%d",&s,&t);


    if(s > 0 && t > 0 && s <= n && t <= n){
        s--;
        t--;
        BFS(s);

        if(D[t] == INF){
            printf("0");
        }else {
            printf("%d",D[t]);
        }
    }else {
        printf("0");
    }


    return 0;
}