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#include<bits/stdc++.h>//submitRecord//
using namespace std;
//const int N=1e7+10;
int main(){
 	//freopen("","r",stdin);
 	//freopen("","w",stdout);
    ios::sync_with_stdio();
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n,m,i;
    cin>>n>>m;
    for(i=m;n>=i;i++) n-=i;
        cout<<i-m;
 	//fclose(stdin);
 	//fclose(stdout);
	return 0;
}