source_code: import java.io.*;
  import java.util.*;
  
  import static java.lang.Math.*;
  
  public class Main {
      static int n, k;
  
      public static void main(String[] args) throws IOException {
          FastScanner sc = new FastScanner();
          PrintWriter pw = new PrintWriter(System.out);
          n = sc.nextInt();
          k = sc.nextInt();
          long l = 0;
          long r = n + 1;
          while (l + 1 != r) {
              long m = (r + l) / 2;
              if (check(m))
                  l = m;
              else
                  r = m;
          }
          pw.print(l * (l + 1L) / 2L - k);
          pw.close();
      }
  
      public static boolean check(long m) {
          return m * (m + 1) / 2 - (n - m) <= k;
      }
  }
  
  class FastScanner {
      static BufferedReader br;
      static StringTokenizer st = new StringTokenizer("");
  
      public FastScanner() {
          br = new BufferedReader(new InputStreamReader(System.in));
      }
  
      public String next() throws IOException {
          while (!st.hasMoreTokens())
              st = new StringTokenizer(br.readLine());
          return st.nextToken();
      }
  
      public int nextInt() throws IOException {
          return Integer.parseInt(next());
      }
  }