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54 lines
1.1 KiB
54 lines
1.1 KiB
#include <bits/stdc++.h>
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using namespace std;
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#define int long long
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#define endl "\n"
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const int N = 2000010;
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int n, mod;
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int primes[N], cnt;
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bool st[N];
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void get_primes(int n) {
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for (int i = 2; i <= n; i++) {
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if (!st[i]) primes[cnt++] = i;
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for (int j = 0; primes[j] * i <= n; j++) {
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st[i * primes[j]] = true;
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if (i % primes[j] == 0) break;
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}
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}
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}
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int qmi(int a, int k) {
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int res = 1;
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while (k) {
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if (k & 1) res = res * a % mod;
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a = a * a % mod;
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k >>= 1;
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}
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return res;
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}
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int get(int n, int p) {
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int s = 0;
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while (n) {
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s += n / p;
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n /= p;
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}
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return s;
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}
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int C(int a, int b) {
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int res = 1;
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for (int i = 0; i < cnt; i++) {
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int p = primes[i];
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int s = get(a, p) - get(b, p) - get(a - b, p);
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res = res * qmi(p, s) % mod;
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}
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return res;
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}
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signed main() {
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cin >> n >> mod;
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get_primes(n * 2);
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cout << (C(n * 2, n) - C(n * 2, n - 1) + mod) % mod << endl;
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} |