/Hóa đơn tiền điện

              #include <iostream>
        using namespace std;
        
        long long getVnd(long long x) {
          if (x > 1000000) return getVnd(1000000) + (x - 1000000) * 700;
          if (x > 10000) return getVnd(10000) + (x - 10000) * 500;
          if (x > 100) return getVnd(100) + (x - 100) * 300;
          return x * 200;
        }
        
        long long getKwh(long long x) {
          if (x > getVnd(1000000)) return 1000000 + (x - getVnd(1000000)) / 700;
          if (x > getVnd(10000)) return 10000 + (x - getVnd(10000)) / 500;
          if (x > getVnd(100)) return 100 + (x - getVnd(100)) / 300;
          return x / 200;
        }
        
        int main() {
          long long x, y;
          cin >> x >> y;
        
          long long total = getKwh(x);
        
          long long low = 0, high = total / 2;
          long long ans = 0;
        
          while (low <= high) {
        
            long long mid = (high + low) / 2;
            long long temp = getVnd(total - mid) - getVnd(mid);
        
            if (temp == y) {
              ans = getVnd(mid);
              break;
            }
            else {
              if (temp < y) high = mid - 1;
              else low = mid + 1;
            }
          }
        
          cout << ans << endl;
        
          return 0;
        }