牛客红包OI赛 C 小可爱表白

据说是个公式题.

Code

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const long long mod = 998244353;

inline long long Pow(long long a, long long b) {
    long long res = 1, base = a;
    while (b) {
        if (b & 1) 
            res = res * base % mod;
        base = base * base % mod;
        b >>= 1;
    }
    return res;
}

long long n, m;
int main() {
    scanf("%lld", &n);
    printf("%lld", n * (n + 1) % mod * Pow(2, n - 2) % mod);
    return 0;
}