Steps

  #include <bits/stdc++.h>
  using namespace std;

  #define cin(vec) for(auto& i : vec) cin >> i
  #define cin_2d(vec, n, m) for(int i = 0; i < n; i++) for(int j = 0; j < m && cin >> vec[i][j]; j++);
  #define cout(vec) for(auto& i : vec) cout << i << " "; cout << "\n";
  #define cout_map(mp) for(auto& [f, s] : mp) cout << f << "  " << s << "\n";
  #define loop(a, b, c) for(int i = a ; i < (b); i += c)
  #define fixed(n) cout << fixed << setprecision(n);
  #define ceil(n, m) (((n) / (m)) + (n % m ? 1 : 0))
  #define all(vec) vec.begin(),vec.end()
  #define rall(vec) vec.rbegin(),vec.rend()
  #define sz size()
  #define fi first
  #define se second
  #define Pair pair <int,int>
  #define ll long long
  #define ull unsigned long long
  #define Mod  1000'000'007
  #define INF 2000'000'000
  #define PI 3.14159265359

  void Code_Crush(){
    ios_base::sync_with_stdio(false);   cin.tie(nullptr);   cout.tie(nullptr);
    #ifndef ONLINE_JUDGE
      freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
  }
  ll n, m, x, y;
  bool valid(ll mid, ll x1, ll y1){
    return ((x + (mid * x1)) <= n && x + (mid * x1) > 0 && (y + (mid * y1)) <= m && (y + (mid * y1)) > 0);
  }
  ll Binary_Search(ll x1, ll y1){
    ll l = 1, r = 1e9, best = 0;
    while(l <= r){
      ll mid = l + (r - l) / 2;
      if(valid(mid, x1, y1)) l = mid + 1, best = mid;
      else r = mid - 1;
    }
    x += best * x1, y += best * y1;
    return best;
  }
  int main(){
    Code_Crush();
    ll k, res = 0;
    cin >> n >> m >> x >> y >> k;
    while(k--){
      ll x1, y1;                  cin >> x1 >> y1;
      res += Binary_Search(x1, y1);
    }
    cout << res << "\n";
    return 0;
  }