#include<bits/stdc++.h>
using namespace std;
const int N= 50050;
vector<pair<int, int>> G[N];
vector<int> p;
bool vis[N];
 
bool dfs(int x)
{
    vis[x]=true;
    int du=0;
    for(auto i:G[x])if(!vis[i.first])
    {
        int y=i.first,id=i.second;
        if(dfs(y))
        {
            du++;
            p.push_back(id);
        }
    }
    return du%2==0;
}
 
int main()
{
    int n,m;scanf("%d%d",&n,&m);
    for(int i=1,x,y;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        G[x].push_back({y,i});
        G[y].push_back({x,i});
    }
    memset(vis,0,sizeof(vis));
    for(int i=1;i<=n;i++)if(!vis[i])
        if(dfs(i))
        {
            printf("-1\n");
            return 0;
        }
    sort(p.begin(),p.end());
    printf("%d\n",p.size());
    for(int i=0;i<p.size();i++)printf("%d\n",p[i]);
    return 0;
}