void main(){
  import std.stdio, std.string, std.conv, std.algorithm;

  int n, k; rd(n, k);
  auto a=readln.split.to!(int[]);

  const int mod=1_000_000_000+7;

  auto rec=new int[][](n+1, k+1);
  for(int i=1; i<=n; i++) rec[i][0]=1;
  for(int i=2; i<=n; i++)for(int j=1; j<=k && j<=i*(i-1)/2; j++){
    (rec[i][j]+=rec[i-1][j])%=mod;
    (rec[i][j]+=rec[i][j-1])%=mod;
    if(j-i>=0) rec[i][j]=(rec[i][j]-rec[i-1][j-i]+mod)%mod;
  }

  writeln(reduce!((r, e)=>(r+e)%mod)(rec[n]));
}

void rd(T...)(ref T x){
  import std.stdio, std.string, std.conv;
  auto l=readln.split;
  assert(l.length==x.length);
  foreach(i, ref e; x){
    e=l[i].to!(typeof(e));
  }
}
void wr(T...)(T x){
  import std.stdio;
  foreach(e; x) stderr.write(e, " ");
  stderr.writeln();
}