1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
#include <bits/stdc++.h>

using namespace std;

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ldbl;
typedef pair<int, int> pii;
typedef pair<uint, uint> puu;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pull;
typedef pair<double, double> pdd;
typedef vector<int> vi;
typedef vector<uint> vu;
typedef vector<ll> vll;
typedef vector<ull> vull;
typedef vector<pii> vpii;
typedef vector<puu> vpuu;
typedef vector<pll> vpll;
typedef vector<pull> vpull;
typedef vector<string> vstr;
typedef vector<double> vdbl;
typedef vector<ldbl> vldbl;
#define pb push_back
#define ppb pop_back
#define pfr push_front
#define ppfr pop_front
#define emp emplace
#define empb emplace_back
#define be begin
#define rbe rbegin
#define all(x) (x).be(), (x).end()
#define rall(x) (x).rbe(), (x).rend()
#define fir first
#define sec second
#define mkp make_pair
#define brif(cond) if (cond) break
#define ctif(cond) if (cond) continue
#define retif(cond) if (cond) return
void canhazfast() {ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);}
template<typename T> T gcd(T a, T b) {return b ? gcd(b, a%b) : a;}
template<typename T> T extgcd(T a, T b, T &x, T &y)
{
    T x0 = 1, y0 = 0, x1 = 0, y1 = 1;
    while (b) {
        T q = a/b; a %= b; swap(a, b);
        x0 -= q*x1; swap(x0, x1);
        y0 -= q*y1; swap(y0, y1);
    }
    x = x0; y = y0; return a;
}
int ctz(uint x) {return __builtin_ctz(x);}
int ctzll(ull x) {return __builtin_ctzll(x);}
int clz(uint x) {return __builtin_clz(x);}
int clzll(ull x) {return __builtin_clzll(x);}
int popcnt(uint x) {return __builtin_popcount(x);}
int popcntll(ull x) {return __builtin_popcountll(x);}
int bsr(uint x) {return 31^clz(x);}
int bsrll(ull x) {return 63^clzll(x);}

#define MOD 1000000007

uint add(uint a, uint b) { return a+b < MOD ? a+b : a+b-MOD; }
uint sub(uint a, uint b) { return a < b ? a+MOD-b : a-b; }
uint mul(uint a, uint b) { return (ull)a*b%MOD; }
uint sqr(uint a) { return mul(a, a); }

uint modpow(uint b, uint e)
{
    uint r = 1;
    for (; e; e >>= 1) {
        if (e&1) r = mul(r, b);
        b = sqr(b);
    }
    return r;
}

uint modpowll(uint b, ull e)
{
    uint r = 1;
    for (; e; e >>= 1) {
        if (e&1) r = mul(r, b);
        b = sqr(b);
    }
    return r;
}

uint modinv(uint n) { return modpow(n, MOD-2); }
uint moddiv(uint n, uint d) { return mul(n, modinv(d)); }

#define N 3072

uint dp[N][2];

int main()
{
    canhazfast();

    int n, m;
    uint ans = 0;

    cin >> n >> m;
    dp[0][0] = 1;
    for (int i = 0; i < n; ++i) {
        for (int j = i; j >= 0; --j) {
            dp[j+1][1] = add(dp[j+1][1], mul(dp[j][0], m-j));
            dp[j][0] = mul(add(dp[j][0], dp[j][1]), j);
            dp[j][1] = mul(dp[j][1], m-j);
        }
    }
    for (int i = 0; i <= n; ++i) ans = add(ans, dp[i][0]);
    cout << ans << '\n';

    return 0;
}