// #pragma GCC target("avx")  // CPU 処理並列化
// #pragma GCC optimize("O3")  // CPU 処理並列化
// #pragma GCC optimize("unroll-loops")  // 条件処理の呼び出しを減らす
// #define BEGIN_STACK_EXTEND(size) void * stack_extend_memory_ = malloc(size);void * stack_extend_origin_memory_;char * stack_extend_dummy_memory_ = (char*)alloca((1+(int)(((long long)stack_extend_memory_)&127))*16);*stack_extend_dummy_memory_ = 0;asm volatile("mov %%rsp, %%rbx\nmov %%rax, %%rsp":"=b"(stack_extend_origin_memory_):"a"((char*)stack_extend_memory_+(size)-1024));
// #define END_STACK_EXTEND asm volatile("mov %%rax, %%rsp"::"a"(stack_extend_origin_memory_));free(stack_extend_memory_);

#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<queue>
#include<deque>
#include<stack>
#include<string>
#include<string.h>
#include<vector>
#include<set>
#include<map>
#include<bitset>
#include<stdlib.h>
#include<cassert>
#include<time.h>
#include<bitset>
#include<numeric>
#include<unordered_set>
#include<unordered_map>
#include<complex>
using namespace std;
const long long mod=998244353;
const long long inf=mod*mod;
const long long d2=(mod+1)/2;
const long double EPS=1e-15;
const long double INF=1e+10;
const double PI=acos(-1.0);
const int C_SIZE = 11100000;
const int UF_SIZE = 3100000;
namespace{
	long long fact[C_SIZE];
	long long finv[C_SIZE];
	long long inv[C_SIZE];
	inline long long Comb(int a,int b){
	 	if(a<b||b<0)return 0;
	 	return fact[a]*finv[b]%mod*finv[a-b]%mod;
	}
	void init_C(int n){
		fact[0]=finv[0]=inv[1]=1;
		for(int i=2;i<n;i++){
			inv[i]=(mod-(mod/i)*inv[mod%i]%mod)%mod;
		}
		for(int i=1;i<n;i++){
			fact[i]=fact[i-1]*i%mod;
			finv[i]=finv[i-1]*inv[i]%mod;
		}
	}
	long long pw(long long a,long long b){
		if(a<0LL)return 0;
		if(b<0LL)return 0;
		long long ret=1;
		while(b){
			if(b%2)ret=ret*a%mod;
			a=a*a%mod;
			b/=2;
		}
		return ret;
	}
	long long pw_mod(long long a,long long b,long long M){
		if(a<0LL)return 0;
		if(b<0LL)return 0;
		long long ret=1;
		while(b){
			if(b%2)ret=ret*a%M;
			a=a*a%M;
			b/=2;
		}
		return ret;
	}
	int pw_mod_int(int a,int b,int M){
		if(a<0)return 0;
		if(b<0)return 0;
		int ret=1;
		while(b){
			if(b%2)ret=(long long)ret*a%M;
			a=(long long)a*a%M;
			b/=2;
		}
		return ret;
	}
	int ABS(int a){return max(a,-a);}
	long long ABS(long long a){return max(a,-a);}
	double ABS(double a){return max(a,-a);}
	int sig(double r) { return (r < -EPS) ? -1 : (r > +EPS) ? +1 : 0; }
	int UF[UF_SIZE];
	void init_UF(int n){
		for(int i=0;i<n;i++)UF[i]=-1;
	}
	int FIND(int a){
		if(UF[a]<0)return a;
		return UF[a]=FIND(UF[a]);
	}
	void UNION(int a,int b){
		a=FIND(a);b=FIND(b);if(a==b)return;
		if(UF[a]>UF[b])swap(a,b);
		UF[a]+=UF[b];UF[b]=a;
	}
}
// ここから編集しろ
long long PW[5100][5100];
int main(){
	for(int i=0;i<5100;i++){
		long long cur=1;
		for(int j=0;j<5100;j++){
			PW[i][j]=cur;
			cur=cur*i%mod;
		}
	}
	int a,b;scanf("%d%d",&a,&b);
	init_C(210000);
	long long ret=0;
	for(int i=1;i<a-1;i++){
		for(int j=1;j<b;j++){
			long long ks=2*j-1;
			ks=ks*PW[b-j][i]%mod;
			ks=ks*(a-i-1)%mod;

			ks=ks*PW[b][a-i-2]%mod;
			ret=(ret+ks)%mod;
			// printf("%d %d: %lld\n",i,j,ks);
		}
	}

	for(int i=1;i<a;i++){
		for(int j=1;j<b;j++){
			long long ks=2;
			ks=ks*PW[b-j][i]%mod;
			ks=ks*PW[b][a-i-1]%mod;
			ret=(ret+ks)%mod;
			// printf("%d %d: %lld\n",i,j,ks);
		}
	}
	ret=(ret+PW[b][a])%mod;
	printf("%lld\n",ret);
}
#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i = 0; i < n; i++)
#define Rep(i,n) for(int i = 1; i <= n; i++)
#define sz(a) int(a.size())
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define debug(a) { cerr << #a << ": " << a << endl; }
#define endl '\n'
#define fi first
#define se second
using lint = long long;
using P = pair<int,int>;
template<class T> using V = vector<T>;
template<class T> using priq     = priority_queue<T>;
template<class T> using priq_inv = priority_queue<T, vector<T>, greater<T>>;
const int dx[] = {0,1,0,-1,1,1,-1,-1};
const int dy[] = {1,0,-1,0,1,-1,-1,1};
template<class T> T ceil(const T &a, const T &b) { return (a+b-1)/b; }
template<class T> bool chmin(T &a, T b) { if(a > b) { a = b; return 1; } return 0; }
template<class T> bool chmax(T &a, T b) { if(a < b) { a = b; return 1; } return 0; }
struct INF { template<class T> operator T() { return numeric_limits<T>::max() / 2; } } INF;

template<class T, class U> istream& operator>>(istream &in, pair<T,U> &p) {
    return in >> p.first >> p.second;
}
template<class T, class U> ostream& operator<<(ostream &out, const pair<T,U> &p) {
    return out << p.first << ' ' << p.second;
}
template<class T> istream& operator>>(istream &in, vector<T> &v) {
    for(auto &&e: v) in >> e;
    return in;
}
template<class T> ostream& operator<<(ostream &out, const vector<T> &v) {
    for(const auto &e: v) out << e << ' ';
    return out;
}

/*----------------------------------------------------------------------------------------------------*/


const lint mod = 1e9+7;

int main() {
    int n;
    cin >> n;
    V<int> a(n);
    cin >> a;
    a.push_back(0);
    sort(all(a));
    lint ans = 1;
    Rep(i,n) {
        ans *= (a[i]-a[i-1]+1);
        ans %= mod;
    }
    cout << ans << endl;
}