View Code of Problem 3692

#include <stdio.h>
int main(){
  int a[50];
  int i;
  int n;
  a[0]=0,a[1]=3,a[2]=6,a[3]=6;
  for(i=4;i<=50;i++)
    a[i]=2*a[i-2]+a[i-1];
  while (scanf("%d",&n)!=EOF){
    printf("%d\n",a[n]);
  }
  return 0;
}