import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
	long n = read.to!long; // how many times she made action
	long k = read.to!long; // how many candies are left at end
	
	foreach(i; 0 .. n + 1){ // how many times she added candies
		long j = n - i; // how many times she ate candies
		long q = i * (i + 1) / 2; // how many candies she added
		log("n:", n, "k:", k, "i:", i, "j:", j, "q:", q);
		if(q == j + k){
			j.writeln;
			return;
		}
	}
	
}
