#include <bits/stdc++.h>

using namespace std;
int n;
vector<int>graff[50050], grev[50050];
map<pair<int, int>, bool> check;
int anc[50050], dist[50050];
bool visited[50050];
vector<int> answer;

void dfs(int v)
{
    visited[v]=true;
    for(int u: graff[v])
    {
        if(!visited[u])
            dfs(u);
    }
    answer.push_back(v);
}

void topological_sort()
{
    for(int i=0; i<=n; i++)visited[i]=false;
    answer.clear();
    for (int i=1; i<=n; ++i)
    {
        if(!visited[i])
            dfs(i);
    }
    reverse(answer.begin(), answer.end());
}

int main()
{
    int m;
    cin>>n>>m;
    for(int i=0; i<m; i++)
    {
        int u, v; cin>>u>>v;
        graff[u].push_back(v);
        grev[v].push_back(u);
        check[{u,v}]=true;
    }
    while(true)
    {
        for(int i=0; i<=n; i++)
        {
            anc[i]=0; dist[i]=0;
        }
        topological_sort();
        for(int k=0; k<answer.size(); k++)
        {
            int i=answer[k];
            for(int j=0; j<grev[i].size(); j++)
            {
                if(check[{grev[i][j],i}])
                {if(dist[grev[i][j]]+1>dist[i]){anc[i]=grev[i][j]; dist[i]=dist[grev[i][j]]+1;}}
            }
        }
        int idmax=0, maks=0;
        bool ans=true;
        for(int i=0; i<=n; i++)
        {
            if(dist[i]>maks){maks=dist[i]; idmax=i;}
        }
        while(true)
        {
            if(anc[idmax]==0){cout<<"! "<<maks<<endl; return 0;}
            cout<<"? "<<anc[idmax]<<" "<<idmax<<endl;
            cin>>ans;
            if(!ans){check[{anc[idmax], idmax}]=false; break;}
            idmax=anc[idmax];
        }
        if(!ans)continue;
    }
    return 0;
}