#include<iostream>

#include<cstring>

#include<cstdio>

#include<algorithm>

#include<cmath>

#define Maxn 3010

#define Maxm 1000000

using namespace std;

int dfn[Maxn],low[Maxn],vi[Maxn],head[Maxn],f[Maxn],e,n,m,lab,top,Stack[Maxn],num,id[Maxn],x[Maxn],y[Maxn];

struct Edge{

    int u,v,next,l;

}edge[Maxm];

void init()

{

    memset(dfn,,sizeof(dfn));

    memset(low,,sizeof(low));

    memset(head,-,sizeof(head));

    memset(id,,sizeof(id));

    e=lab=num=top=;

}

void add(int u,int v)

{

    edge[e].u=u,edge[e].v=v,edge[e].next=head[u],head[u]=e++;

}

void Tarjan(int u)

{

    int i,j,v;

    dfn[u]=low[u]=++lab;

    Stack[top++]=u;

    vi[u]=;

    for(i=head[u];i!=-;i=edge[i].next)

    {

        v=edge[i].v;

        if(!dfn[v])

        {

            Tarjan(v);

            low[u]=min(low[u],low[v]);

        }

        if(vi[v])

        low[u]=min(low[u],dfn[v]);

    }

    if(low[u]==dfn[u])

    {

        ++num;

        do{

            i=Stack[--top];

            vi[i]=;

            id[i]=num;

        }while(i!=u);

    }

}

int solve(int mid)

{

    int i,j;

    init();

    for(i=;i<=mid;i++)

    {

        add(f[x[i]],y[i]);

        add(f[y[i]],x[i]);

    }

    for(i=;i<=n;i++)

        if(!dfn[i])

        {

            Tarjan(i);

        }

    for(i=;i<=n;i++)

    {

        if(id[i]==id[f[i]])

            return ;

    }

    return ;

}

int main()

{

    int i,j,a,b;

    while(scanf("%d%d",&n,&m),n|m)

    {

        init();

        memset(f,,sizeof(f));

        for(i=;i<=n;i++)

        {

            scanf("%d%d",&a,&b);

            a++,b++;

            f[a]=b,f[b]=a;

        }

        for(i=;i<=m;i++)

        {

            scanf("%d%d",x+i,y+i);

            x[i]++,y[i]++;

        }

        n*=;

        int l,r,mid;

        l=,r=m+;

        while(r>l+)

        {

            mid=(l+r)>>;

            if(solve(mid))

                l=mid;

            else

                r=mid;

        }

        printf("%d\n",l);

    }

    return ;

}