#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
    #include <atcoder/all>
using namespace atcoder;
#endif
template<class T, class... Ts> void print(const T& a, const Ts&... b){cout << a;(cout << ... << (cout << ' ', b));cout << '\n';}
template<class... T> void input(T&... a){(cin >> ... >> a);}
void print(){cout << '\n';}
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
typedef modint998244353 mint;
#define rep(i, n) for(ll i = 0; i < n; i++)

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    ll n,m; input(n,m);
    if(n < m)return print(0),0;
    mint ans = ((mint)n-(mint)m+1)*((mint)n-(mint)m+2)/2;
    print(ans.val());
    
    return 0;
}