#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef long long ll; typedef vector vl; typedef vector> vvl; typedef pair P; #define rep(i, n) for(ll i = 0; i < n; i++) #define exrep(i, a, b) for(ll i = a; i <= b; i++) #define out(x) cout << x << endl #define exout(x) printf("%.10f\n", x) #define chmax(x, y) x = max(x, y) #define chmin(x, y) x = min(x, y) #define all(a) a.begin(), a.end() #define rall(a) a.rbegin(), a.rend() #define pb push_back #define re0 return 0 const ll mod = 1000000007; const ll INF = 1e16; const ll MAX = 1000010; ll fact[MAX]; // fact[i] : iの階乗のmod ll inv[MAX]; // inv[i] : iの逆数のmod ll invfact[MAX]; // invfact[i] : iの階乗の逆数のmod void init() { fact[0] = 1; inv[0] = inv[1] = 1; invfact[0] = 1; for(ll i = 1; i < MAX; i++) { fact[i] = i * fact[i-1] % mod; if(i >= 2) { inv[i] = mod - inv[mod % i] * (mod / i) % mod; } invfact[i] = invfact[i-1] * inv[i] % mod; } } // nCrをO(n)で求める。 ll Comb(ll n, ll r) { if(r < 0 || n < 0 || n < r) { return 0; } ll res = fact[n]; res = (res * invfact[r]) % mod; res = (res * invfact[n - r]) % mod; return res; } int main() { ll n, m; cin >> n >> m; if(n == 1 || m == 1) { out(1); re0; } init(); vl vec(2*m + 1); ll flag = 1; // 増加するなら1 ll x = 1; for(ll i = m-2; i >= 0; i--) { vec[i] = x; if(x == 0 || x == n-1) { flag = 1 - flag; if(i > 0) { i--; vec[i] = x; } } if(flag) { x++; } else { x--; } } flag = 1; x = 1; exrep(i, m+1, 2*m) { vec[i] = x; if(x == 0 || x == n-1) { flag = 1 - flag; if(i < 2*m) { i++; vec[i] = x; } } if(flag) { x++; } else { x--; } } vl f(2*m + 1); // f[x] : 左右移動をm回繰り返して、位置x-mにいる場合の数 exrep(i, 0, m) { f[2*i] = Comb(m, i); } ll ans = 0; exrep(i, 0, 2*m) { if(vec[i] == 0) { ans += f[i]; ans %= mod; } } out(ans); re0; }