import std.stdio, std.array, std.string, std.conv, std.algorithm; import std.typecons, std.range, std.random, std.math, std.container; import std.numeric, std.bigint, core.bitop, core.stdc.stdio; immutable long MAX = 2*10^^6+1; immutable long MOD = 10^^9+7; long powmod(long a, long x, long m) { a %= m; long ret = 1; while (x) { if (x % 2) ret = ret * a % m; a = a * a % m; x /= 2; } return ret; } void main() { auto modinv = new long[](MAX); modinv[0] = modinv[1] = 1; foreach(i; 2..MAX) { modinv[i] = modinv[MOD % i] * (MOD - MOD / i) % MOD; } auto f_mod = new long[](MAX); auto f_modinv = new long[](MAX); f_mod[0] = f_mod[1] = 1; f_modinv[0] = f_modinv[1] = 1; foreach(i; 2..MAX) { f_mod[i] = (i * f_mod[i-1]) % MOD; f_modinv[i] = (modinv[i] * f_modinv[i-1]) % MOD; } long nck(long n, long k) { return f_mod[n] * f_modinv[n-k] % MOD * f_modinv[k] % MOD; } auto s = readln.split.map!(to!long); auto N = s[0]; auto M = s[1]; long ans = 0; foreach (i; 0..M) { long p = nck(M, i) * powmod(M-i, N, MOD) % MOD; if (i % 2 == 0) ans = (ans + p) % MOD; else { ans = (ans - p) % MOD; ans = (ans + MOD) % MOD; } } writeln((ans + MOD) % MOD); }