source_code: import java.util.*;
  import java.io.*;
  
  public class B {
  	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  	static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
  	
  	public static void main(String[] args) throws Exception {
  		String[] split = br.readLine().split(" ");
  		
  		long n = Long.parseLong(split[0]);
  		long k = Long.parseLong(split[1]);
  		
  		long left = -1;
  		long right = n + 1;
  		
  		while(right - left >= 2) {
  			long mid = (left + right) / 2; // 10
  			// if(mid > n) {
  				// right = mid;
  				// continue;
  			// }
  			
  			long newN = n - mid; //-5
  			long temp = newN * (newN + 1) / 2; //10
  			
  			long eh = temp - k - mid;
  			
  			if(eh == 0) {
  				pw.println(mid);
  				break;
  			}
  			else if(eh < 0)
  				right = mid;
  			else
  				left = mid;
  		}
  		
  		pw.close();
  	}
  }