#include<bits/stdc++.h>
#define ll long long
#define il inline
#define pn putchar('\n')
#define maxint 2147483647
#define min(x,y) (x<y?x:y)
#define max(x,y) (x>y?x:y)
#define maxn 500005
using namespace std;
int n,q,sq=200,idx;
int a[maxn<<1],fr[maxn],ind[maxn],si[maxn],g[2501][2501];
bitset<1000001>f[2501];
signed main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
    freopen("out.txt","w",stdout);
    #endif
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&si[i]);
        fr[i]=fr[i-1]+si[i-1];
        for(int j=0;j<si[i];j++)
        {
            int x;
            scanf("%d",&x);
            a[fr[i]+j]=x;
        }
        if(si[i]<=sq)
            sort(a+fr[i],a+fr[i]+si[i]);
        else
        {
            ind[i]=++idx;
            for(int j=0;j<si[i];j++)
                f[idx][a[fr[i]+j]]=1;
            for(int j=1;j<idx;j++)
            {
                bool fl=0;
                for(int k=0;k<si[i];k++)
                {
                    if(f[j][a[fr[i]+k]])
                    {
                        fl=1;
                        g[j][idx]=g[idx][j]=a[fr[i]+k];
                        break;
                    }
                }
                if(!fl)
                    g[j][idx]=g[idx][j]=-1;
            }
        }
    }
    while(q--)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        if(si[x]>si[y])
            swap(x,y);
        if(si[x]>sq)
            printf("%d\n",g[ind[x]][ind[y]]);
        else if(si[y]>sq)
        {
            bool fl=0;
            for(int i=0;i<si[x];i++)
            {
                if(f[ind[y]][a[fr[x]+i]])
                {
                    fl=1,printf("%d\n",a[fr[x]+i]);
                    break;
                }
            }
            if(!fl)
                puts("-1");
        }
        else
        {
            bool fl=0;
            for(int i=0,j=0;i<si[x];i++)
            {
                while(j<si[y]&&a[fr[y]+j]<a[fr[x]+i])j++;
                if(j<si[y]&&a[fr[x]+i]==a[fr[y]+j])
                {
                    fl=1;
                    printf("%d\n",a[fr[x]+i]);
                    break;
                }
            }
            if(!fl)
                puts("-1");
        }
    }
    return 0;
}