坤你太美

很复杂：

#include<bits/stdc++.h>
#include<iostream>
#include<cmath>
#define kunuse using
#define kunspace namespace
#define KUNTD std
#define zhiyinint int
#define zhiyinfloat double
#define zhiyinchar char
#define zhiyinstring string
#define zhiyinbool bool
#define zhiyinvoid void
#define kuntruct struct
#define IKUN main
#define kunin cin
#define kunout cout
#define kundl endl
#define kunfor for
#define kunif if
#define kunelif else if
#define kunelse else
#define xiaoheizi0 false
#define xiaoheizi1 true
#define kunturn return
using namespace std;

long long f(int n){
    if(n<=3) return 1;
    else return f(n-1)+2*f(n-3);
}

int main(){
    int n;
    cin>>n;
    cout<<f(n);

    return 0;
}