import java.io.*;
import java.util.*;


class Main {
    static final long MOD=1000000007;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int k=sc.nextInt();
        int s=n*(n-1)/2+1;
        long[][]dp=new long[2][s];
        dp[0][0]=1;
        for(int i=0;i<n;++i){
            int u=i%2;
            int nxt=1-u;
            Arrays.fill(dp[nxt],0);
            for(int j=0;j<s;++j){
                if(j+i+1<s)
                    dp[nxt][j+i+1]=(dp[nxt][j+i+1]-dp[u][j]+MOD)%MOD;
                dp[nxt][j]=(dp[nxt][j]+dp[u][j])%MOD;
            }
            for(int j=1;j<s;++j)
                dp[nxt][j]=(dp[nxt][j]+dp[nxt][j-1])%MOD;
        }
        long ans=0;
        for(int i=0;i<=k;++i)
            ans=(ans+dp[n%2][i])%MOD;
        System.out.println(ans);
    }
}