source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.StringTokenizer;
  
  public class Cf2 {
  
      static boolean ok(long n, long k, long eatten) {
          long moves = n-eatten;
          long ans = moves*(moves+1)/2;
          ans -= eatten;
          return ans <= k;
      }
  
      public static void main(String[] args) {
          FastReader in = new FastReader();
          long n = in.nextInt();
          long k = in.nextInt();
          long left = 0, right = n;
          while (left <= right) {
              long middle = (left+right)/2;
              if (ok(n, k, middle)) right = middle-1;
              else left=middle+1;
          }
          System.out.println(left);
      }
  
      static class FastReader
      {
          BufferedReader br;
          StringTokenizer st;
  
          public FastReader() {
              br = new BufferedReader(new
                      InputStreamReader(System.in));
          }
  
          String next()
          {
              while (st == null || !st.hasMoreElements())
              {
                  try
                  {
                      st = new StringTokenizer(br.readLine());
                  }
                  catch (IOException e)
                  {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
  
          int nextInt()
          {
              return Integer.parseInt(next());
          }
  
          long nextLong()
          {
              return Long.parseLong(next());
          }
  
          double nextDouble()
          {
              return Double.parseDouble(next());
          }
  
          String nextLine()
          {
              String str = "";
              try
              {
                  str = br.readLine();
              }
              catch (IOException e)
              {
                  e.printStackTrace();
              }
              return str;
          }
      }
  }
  