#include <iostream>
#include <cassert>
#include <vector>
using namespace std;
int main(){
	long long n, m;
	cin >> n >> m;

	vector<long long> p(n);
	for(auto& x : p) x = rand();

	vector<vector<pair<int,int>>> g(n);
	int inc = 0, dec = 0;
	for(int i = 1; i <= m; ++i){
		int u,v; cin >> u >> v;
		--u, --v;
		assert(u!=v);
		g[u].push_back({v,i});
		if(p[v] > p[u]) ++inc; else ++dec;
	}

	if(inc < dec){
		cout << inc << endl;
		for(int u = 0; u < n; ++u)
			for(auto e : g[u]){
				if(p[e.first] > p[u])
					cout << e.second << endl;
			}
	} else {
		cout << dec << endl;
		for(int u = 0; u < n; ++u)
			for(auto e : g[u]){
				if(p[e.first] < p[u])
					cout << e.second << endl;
			}
	}
}