#include <bits/stdc++.h>
using namespace std;
int w;
pair<int, int> dfs() {
  int m, n;
  cin >> m >> n;
  vector<pair<int, int>> arr;
  while(n--) arr.push_back(dfs());
  sort(arr.begin(), arr.end());
  int rem = 0, tot = 0;
  for(auto it : arr) tot += it.second;
  for(auto it : arr)
    if(rem + it.first <= w) rem += it.first, tot--;
    else break;
  rem += m;
  tot += (rem + w - 1) / w, rem %= w;
  if(!rem) rem = w;
  return {rem, tot};
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  #ifdef ALEX_WEI
    FILE* IN = freopen("1.in", "r", stdin);
    FILE* OUT = freopen("1.out", "w", stdout);
  #endif
  cin >> w;
  cout << dfs().second << "\n";
  cerr << 1e3 * clock() / CLOCKS_PER_SEC << " ms\n";
  return 0;
}
/*
g++ D.cpp -o D -std=c++14 -O2 -DALEX_WEI
*/