2641.cpp

#include <stdio.h>

int n,sum;

void dfs(int k, int p1, int p2){
    if(k>n) return;
    if(k==n) {
        sum++; return;
    }
    if((p1==3) or (p2==3)){
        dfs(k+1,p2,1);
        dfs(k+2,p2,2);
    }
    else{
    dfs(k+1,p2,1);
    dfs(k+2,p2,2);
    dfs(k+3,p2,3);
    }
}

int main(){
    scanf("%d", &n);
    
    dfs(0,0,0);
    
    printf("%d", sum);
    return 0;
}