#include <bits/stdc++.h>
using namespace std;
#ifdef MIKU
string dbmc = "\033[1;38;2;57;197;187m", dbrs = "\033[0m";
#define debug(x...) cout << dbmc << "[" << #x << "]: ", dout(x)
void dout() { cout << dbrs << endl; }
template <typename T, typename ...U>
void dout(T t, U ...u) { cout << t << (sizeof...(u) ? ", " : ""); dout(u...); }
#else
#define debug(...) 39
#endif
#define fs first
#define sc second
#define mp make_pair
#define FOR(i, j, k) for (int i = j, Z = k; i < Z; i++)
using ll = long long;
typedef pair<int, int> pii;
const int MXN = 500005;
int n, m;
vector<int> edge[MXN];
bitset<MXN> ban;
vector<int> ans;
void miku() {
int x, y;
cin >> n >> m;
while (m--) {
cin >> x >> y;
edge[x].push_back(y);
edge[y].push_back(x);
}
FOR(id, 1, n + 1) {
if (ban[id]) continue;
ans.push_back(id);
for (auto &i : edge[id]) ban[i] = true;
}
cout << ans.size() << '\n';
for (auto &i : ans) cout << i << ' ';
cout << '\n';
}
int32_t main() {
cin.tie(0) -> sync_with_stdio(false);
cin.exceptions(cin.failbit);
miku();
return 0;
}
