题解 | 大吉大利，今晚吃鸡

#include <stdio.h>
int f(int n,char kaishi,char mid,char end)
{
    int count=0;
    if(n==1)
    {
        count+=2;
        return count;
    }
    int sum=0;
    sum+=f(n-1,kaishi,mid,end);
    sum++;
    sum+=f(n-1,end,mid,kaishi);
    sum++;
    sum+=f(n-1,kaishi,mid,end);
    return sum;


}
int main() {
    int n;
    
    while(scanf("%d",&n)!=EOF)
    {
       int count=f(n,'f','m','e');
       printf("%d\n",count);
    }
    return 0;
}