神秘 WA 求调

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

const ll N = 500005 , mod = 1000000007 , _2 = mod + 1 >> 1;
ll fpow(ll aa , ll bb)
{
    ll res = 1;
    while(bb)
    {
        if(bb & 1) res = res * aa % mod;
        aa = aa * aa % mod; bb >>= 1;
    }
    return res;
}
ll W(ll k) {return k >= mod ? k - mod : k;}

signed main()
{
	ll n , m; cin >> n >> m;
	if(n <= m)
	{
		ll fi[N] , f[N] , g[N]; fi[0] = g[0] = 1;
		for(ll i = 1 ; i <= n ; i++)
		{
			fi[i] = W(fi[i - 1] + (i > 1 ? fi[i - 2] : 0));
			f[i] = g[i] = fpow(fi[i] , m);
			for(ll j = 0 ; j < i ; j++) f[i] = (f[i] + (mod - f[j]) * g[i - j]) % mod;
		}
		cout << f[n] << endl;
	}
	else
	{
		ll f[N] , fac[N] , ifac[N] , fi[N] , d = 0;
		fac[0] = 1;for(ll i = 1 ; i < N ; i++) fac[i] = fac[i - 1] * i % mod;
		ifac[N - 1] = fpow(fac[N - 1] , mod - 2);
		for(ll i = N - 1 ; i ; i--) ifac[i - 1] = i * ifac[i] % mod;
		if(m % 2 == 0)
		{
			d = 1; f[0] = (m % 4) ? 1 : mod - 1;
			f[1] = 1;
		}
		else f[0] = 1;
		for(ll i = 2 - (m & 1) ; i <= m ; i += 2)
		{
			ll cur = 0;
			for(ll j = 0 , t = fac[i] ; j <= i ; j += 2 , t = 5ll * t % mod)
				cur = (cur + t * ifac[j] % mod * ifac[i - j]) % mod;
			cur = cur * fpow(_2 , i - 1) % mod;
			ll b(((m - i) % 4) ? cur : mod - cur) , g[N];
			for(ll t = 0 ; t <= d + 2 ; t++)
			{
				ull num((m & 1) ? mod - f[t] : f[t]);
				if(t) num += b * f[t - 1];
				if(t > 1) num += f[t - 2];
				g[t] = num % mod;
			}
			d += 2;
			copy(g , g + d + 1 , f);
		}
		reverse(f , f + d + 1);
		ll F[N] , H[N];
		for(ll i = 0 ; i < d ; i++)
		{
			if(i < 2) fi[i] = 1;
			else fi[i] = W(fi[i - 1] + fi[i - 2]);
			F[i] = fpow(fi[i] , m);
		}
		for(ll i = 0 ; i < d ; i++) for(ll j = 0 ; j <= i ; j++)
			H[i] = (H[i] + f[j] * F[i - j]) % mod;
		ll iv(fpow(H[0] , mod - 2));
		for(ll i = 0 ; i <= n ; i++)
		{
			ll v = f[i];
			for(ll j = 1 ; j <= i && j < d ; j++) v = (v + (mod - f[i - j]) * H[j]) % mod;
			f[i] = v * iv % mod;
		}
		cout << (mod - f[n]) % mod << endl;
	}
	return 0;
}