#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
const int BUFFER_SIZE = 1 << 18;
const int INF = 1 << 30;
const long long LINF = 1ll << 60;
char BUFFER[BUFFER_SIZE];
int gi() {
  int x;
  scanf("%d", &x);
  return x;
}
double gd() {
  double x;
  scanf("%lf", &x);
  return x;
}
long long gll() {
  long long x;
  cin >> x;
  return x;
}
vector<int> gvi(int n) {
  vector<int> a;
  while (n--) a.push_back(gi());
  return a;
}
string gs() {
  scanf("%s", BUFFER);
  return string(BUFFER);
}
istringstream buff() { return istringstream(string(BUFFER)); }
template <class T>
struct forArray {
  T* a;
  int n;
  forArray(T* a, int n) : a(a), n(n) {}
};
template <class A, class B>
ostream& operator<<(ostream& os, const pair<A, B>& d);
template <class T>
ostream& operator<<(ostream& os, const vector<T>& d);
template <class T>
ostream& operator<<(ostream& os, const queue<T>& d);
template <class T>
ostream& operator<<(ostream& os, const stack<T>& d);
template <class T>
ostream& operator<<(ostream& os, const set<T>& d);
template <class T>
ostream& operator<<(ostream& os, const multiset<T>& d);
template <class T>
ostream& operator<<(ostream& os, const unordered_set<T>& d);
template <class A, class B>
ostream& operator<<(ostream& os, const map<A, B>& d);
template <class A, class B>
ostream& operator<<(ostream& os, const multimap<A, B>& d);
template <class A, class B>
ostream& operator<<(ostream& os, const unordered_map<A, B>& d);
template <class T>
ostream& operator<<(ostream& os, const vector<T>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class T>
ostream& operator<<(ostream& os, const queue<T>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class T>
ostream& operator<<(ostream& os, const stack<T>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class T>
ostream& operator<<(ostream& os, const set<T>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class T>
ostream& operator<<(ostream& os, const multiset<T>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class T>
ostream& operator<<(ostream& os, const unordered_set<T>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class A, class B>
ostream& operator<<(ostream& os, const map<A, B>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class A, class B>
ostream& operator<<(ostream& os, const multimap<A, B>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class A, class B>
ostream& operator<<(ostream& os, const unordered_map<A, B>& d) {
  os << "[";
  int f = 0;
  for (auto x : d) {
    if (f) os << ",";
    f = 1;
    os << x;
  }
  return os << "]";
};
template <class T>
ostream& operator<<(ostream& os, const forArray<T>& d) {
  os << "[";
  for (int i = 0; i < d.n; ++i) {
    if (i) os << ",";
    os << d.a[i];
  }
  return os << "]";
}
template <class A, class B>
ostream& operator<<(ostream& os, const pair<A, B>& d) {
  return os << "[" << d.first << ", " << d.second << "]";
}
int main() {
  int n = gi();
  int m = gi();
  vector<pair<pair<int, int>, int>> Q;
  for (int i = 0; i < m; ++i) {
    int r = gi();
    int c = gi();
    Q.push_back({{n - r, c - 1}, i});
  }
  sort((Q).begin(), (Q).end());
  vector<int> res;
  int p = 0;
  set<pair<int, int>> S;
  for (int i = 0; i < n; ++i) {
    while (p < Q.size() && Q[p].first.first <= i)
      S.insert({Q[p].first.second, Q[p].second}), ++p;
    while (S.size() && S.begin()->first < i) S.erase(S.begin());
    if (S.size()) {
      res.push_back(S.begin()->second);
      S.erase(S.begin());
    }
  }
  sort((res).begin(), (res).end());
  printf("%d\n", res.size());
  for (int i = 0; i < res.size(); ++i)
    printf("%d%c", res[i] + 1, i + 1 == res.size() ? '\n' : ' ');
  return 0;
}
