#include using namespace std; using namespace std::chrono; using ll=long long; using ull=unsigned long long; using uint=unsigned int; using pii=pair; using pll=pair; using pdd=pair; const ll LINF=0x3fffffffffffffff; const ll MOD=1000000007; const ll MODD=0x3b800001; const int INF=0x3fffffff; const double DINF=numeric_limits::infinity(); const vector four={{-1,0},{0,1},{1,0},{0,-1}}; #define _overload4(_1,_2,_3,_4,name,...) name #define _overload3(_1,_2,_3,name,...) name #define _rep1(n) _rep2(i,n) #define _rep2(i,n) _rep3(i,0,n) #define _rep3(i,a,b) for(ll i=a;i=a;i--) #define _rrep4(i,a,b,c) for(ll i=a+(b-a-1)/c*c;i>=a;i-=c) #define rrep(...) _overload4(__VA_ARGS__,_rrep4,_rrep3,_rrep2,_rrep1)(__VA_ARGS__) #define each(i,a) for(auto&& i:a) #define sum(...) accumulate(range(__VA_ARGS__),0LL) #define dsum(...) accumulate(range(__VA_ARGS__),double(0)) #define _range(i) (i).begin(),(i).end() #define _range2(i,k) (i).begin(),(i).begin()+k #define _range3(i,a,b) (i).begin()+a,(i).begin()+b #define range(...) _overload3(__VA_ARGS__,_range3,_range2,_range)(__VA_ARGS__) #define yes(i) out(i?"yes":"no") #define Yes(i) out(i?"Yes":"No") #define YES(i) out(i?"YES":"NO") #define elif else if #define unless(a) if(!(a)) #define mp make_pair #define INT(...) int __VA_ARGS__;in(__VA_ARGS__) #define LL(...) ll __VA_ARGS__;in(__VA_ARGS__) #define STR(...) string __VA_ARGS__;in(__VA_ARGS__) #define CHR(...) char __VA_ARGS__;in(__VA_ARGS__) #define DBL(...) double __VA_ARGS__;in(__VA_ARGS__) #define vec(type,name,...) vector name(__VA_ARGS__) #define VEC(type,name,size) vector name(size);in(name) #define vv(type,name,h,...) vector>name(h,vector(__VA_ARGS__)) #define VV(type,name,h,...) vector>name(h,vector(__VA_ARGS__));in(name) __attribute__((constructor)) void SETTINGS(){cin.tie(0); cout.tie(0); ios::sync_with_stdio(0); cout< inline constexpr T gcd (T a,T b) {if(a==b)return a;else return gcd(b,(a-1)%b+1);} template inline constexpr T lcm (T a,T b) {a*b/gcd(a,b);} template inline constexpr T min(vector& v){return *min_element(range(v));} inline char min(string& v){return *min_element(range(v));} template inline constexpr T max(vector& v){return *max_element(range(v));} inline char max(string& v){return *max_element(range(v));} template inline bool update_min(T& mn,const T& cnt){if(mn>cnt){mn=cnt;return 1;}else return 0;} template inline bool update_max(T& mx,const T& cnt){if(mx istream& operator >> (istream& is, vector& vec); template istream& operator >> (istream& is, array& vec); template istream& operator >> (istream& is, pair& p); template ostream& operator << (ostream& os, vector& vec); template ostream& operator << (ostream& os, pair& p); template istream& operator >> (istream& is, vector& vec){for(T& x: vec) is >> x;return is;} template istream& operator >> (istream& is, pair& p){is >> p.first;is >> p.second;return is;} template ostream& operator << (ostream& os, vector& vec){os << vec[0];rep(i,1,vec.size()){os << ' ' << vec[i];}return os;} template ostream& operator << (ostream& os, deque& deq){os << deq[0];rep(i,1,deq.size()){os << ' ' << deq[i];}return os;} template ostream& operator << (ostream& os, pair& p){os << p.first << " " << p.second;return os;} template pair operator + (pair a, pair b){return {a.first + b.first, a.second + b.second};} template inline void in(Head&& head,Tail&&... tail){cin>>head;in(move(tail)...);} template inline void out(T t){cout< inline void out(Head head,Tail... tail){cout< inline void err(T t){cerr< inline void err(Head head,Tail... tail){cerr<=MOD)sum-=MOD; ans=(ans+sum*b[n-i])%MOD; } printf("%lld\n",ans); }