D. Radio Towers

手算前7项 1/2,1/4,2/8,3/16,5/32,8/64…
分子斐波那契，分母2^n

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=2e5+10;
const int mod=998244353;
ll base[maxn];
void init()
{
    base[1]=1;
    base[2]=1;
    for(int i=3;i<=maxn-10;i++){
        base[i]=(base[i-1]+base[i-2])%mod;
    }
}
ll quick(ll a,ll b)
{
    ll ans=1;
    while(b>0){
        if(b%2!=0) ans=ans*a%mod;
        a=a*a%mod;
        b=b/2;
    }
    return ans;
}
void ex_gcd(ll a, ll b, ll &x, ll &y, ll &d){
    if (!b) {d = a, x = 1, y = 0;}
    else{
        ex_gcd(b, a % b, y, x, d);
        y -= x * (a / b);
    }
}
ll inv(ll t, ll p){//如果不存在，返回-1
    ll d, x, y;
    ex_gcd(t, p, x, y, d);
    return d == 1 ? (x % p + p) % p : -1;
}
//int main(){
//    LL a, p;
//    while(~scanf("%lld%lld", &a, &p)){
//        printf("%lld\n", inv(a, p));
//    }
//}
int main()
{
    init();
    ll n;
    scanf("%lld",&n);
    ll tmp=quick(2,n);
   // printf("%lld\n",tmp);
    ll ans=base[n]*inv(tmp,mod)%mod;
    printf("%lld\n",ans);
    return 0;
}