【模拟试题】微小的数学

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll mod=998244353LL;
ll n,s,d;
ll mul(ll a,ll b){return a%mod*(b%mod)%mod;}
ll ksm(ll a,ll b){
    a%=mod;ll ret=1LL;
    while(b){
        if(b&1)ret=ret*a%mod;
        a=a*a%mod,b>>=1;
    }
    return ret;
}
int main()
{
    scanf("%lld%lld%lld",&n,&s,&d);
    printf("%lld",(mul(s,ksm(2LL,n))+mul(mul(n,d),ksm(2LL,n-1)))%mod);
}