#include #pragma GCC target("avx") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") using namespace std; #define rep(i, n) for(long long i=0;i<(long long)(n);i++) #define REP(i,k,n) for(long long i=k;i<(long long)(n);i++) #define pb emplace_back #define lb(v,k) (lower_bound(all(v),(k))-v.begin()) #define ub(v,k) (upper_bound(all(v),(k))-v.begin()) #define fi first #define se second #define pi M_PI #define PQ(T) priority_queue #define SPQ(T) priority_queue,greater> #define dame(a) {out(a);return 0;} #define decimal cout< P; typedef tuple PP; typedef tuple PPP; using vi=vector; using vvi=vector; using vvvi=vector; using vvvvi=vector; using vp=vector

; using vvp=vector; using vb=vector; using vvb=vector; const ll inf=1001001001001001001; const ll INF=1001001001; const ll mod=1000000007; const double eps=1e-10; template bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;} template bool chmax(T&a,T b){if(a void out(T a){cout< void outp(T a){cout<<'('< void outvp(T v){rep(i,v.size())cout<<'('< void outvvp(T v){rep(i,v.size())outvp(v[i]);} template void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout< void outvv(T v){rep(i,v.size())outv(v[i]);} template bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);} template void yesno(T b){if(b)out("yes");else out("no");} template void YesNo(T b){if(b)out("Yes");else out("No");} template void YESNO(T b){if(b)out("YES");else out("NO");} template void outset(T s){auto itr=s.begin();while(itr!=s.end()){if(itr!=s.begin())cout<<' ';cout<<*itr;itr++;}cout<<'\n';} void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);} ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);} ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;} vi fac,finv,inv; void init(ll n){ n*=3; fac=vi(n+5);finv=vi(n+5);inv=vi(n+5); fac[0] = fac[1] = 1; finv[0] = finv[1] = 1; inv[1] = 1; REP(i,2,n+5){ fac[i]=fac[i-1]*i%mod; inv[i]=mod-inv[mod%i]*(mod/i)%mod; finv[i]=finv[i-1]*inv[i]%mod; } } long long modcom(ll n, ll k){ if (n < k) return 0; if (n < 0 || k < 0) return 0; return fac[n] * (finv[k] * finv[n - k] % mod) % mod; } int main(){ ll n,K;cin>>n>>K;init(n+K); ll ans=0; rep(i,n)ans+=modcom(n-1,i)*modcom(n+K-1-i,n)%mod; out(ans%mod); }