"use strict";
    
// 組み合わせ（nCr）列挙ではなく計算のみ
const permutation = (n, r) => {
    let res = 1;
    
    for(let i=0; i<r; i++) {
        res *= n - i;
    }
    
    return res;
}
 
const nCr = (n, r) => {
    return permutation(n, r) / permutation(r, r);
}

const main = arg => {
    arg = arg.trim().split("\n");
    const N = parseInt(arg[0].split(" ")[0]);
    const K = parseInt(arg[0].split(" ")[1]);
    const MOD = 10e9 + 7;
    
    let answer = 0;
 
    for(let i=K; i<=N+1; i++) {
        let temp = ((N - i) * (N - i + 1)) / 2;
        let comb;
        
        if(N+1 === i) {
            comb = 1;
        } else {
            comb = nCr(N + 1, i);
        }

        // console.log("i;" + i);
        // console.log("comb;" + comb);
        // console.log("temp;" + temp);
        
        answer += (comb - temp) % MOD;
    }
    
    console.log(answer)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));