#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
const ll mod = 1000000007;
int main() {
  int n, k;
  cin >> n >> k;
  vector<int> L(k);
  vector<int> R(k);
  for (int i = 0; i < (k); ++i) {
    cin >> L[i] >> R[i];
  }
  vector<int> dp(n, 0);
  vector<ll> dpsum(n, 0);
  dpsum[0] = 1;
  dp[0] = 1;
  for (int i = 1; i < n; i++) {
    for (int j = 0; j < (k); ++j) {
      if (i - L[j] < 0) {
        continue;
      } else if (i - R[i - 1] < 0) {
        dp[i] += dpsum[i - L[j]];
      } else {
        dp[i] += dpsum[i - L[j]] - dpsum[i - R[j] - 1];
      }
    }
    dpsum[i] = dpsum[i - 1] + dp[i];
  }
  cout << dp[n - 1] << endl;
}
