import std;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] lreads(T = long)(long n){return generate(()=>readln.chomp.to!T()).take(n).array();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);
// dfmt on

void main()
{
    long N, K;
    scan(N, K);
    auto s = new long[](N + 2);
    foreach (i; 0 .. N + 1)
    {
        s[i + 1] += s[i] + i;
    }
    long ans;
    foreach (i; K .. N + 1)
    {
        ans = (ans + (s[$ - 1] - s[$ - i - 1]) - (s[i]) + 1) % MOD;
    }
    writeln(ans + 1);
}
