题目描述
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 100010, mod = 1e9 + 7;
int qmi(int a, int k, int p)
{
int res = 1;
while (k)
{
if (k & 1) res = (LL)res * a % p;
a = (LL)a * a % p;
k >>= 1;
}
return res;
}
int main()
{
int n;
scanf("%d",&n);
int a = n * 2, b = n;
int res = 1;
for (int i = a; i > a - b; i -- ) res = (LL)res * i % mod;
for (int i = 1; i <= b; i ++ ) res = (LL)res * qmi(i, mod - 2, mod) % mod;
res = (LL)res * qmi(n + 1, mod - 2, mod) % mod;
printf("%d\n",res);
return 0;
}