memset(dp,0,sizeof(dp));

// 0 - red, 1 - blue, 2 - white

dp[0][0] = 1;

dp[0][1] = 0;

dp[0][2] = 1;

for(int i=1; i<N; i++){

for(int color = 0; color < 3; color++){

for(int pre_c = 0; pre_c<3; pre_c++){

if(color==pre_c)continue;

if(color==1){

if(pre_c==0){

dp[i+1][2] += dp[i-1][pre_c];

}else if(pre_c==2){

dp[i+1][0] += dp[i-1][pre_c];

}

}else{

dp[i][color] += dp[i-1][pre_c];

}

}

}

}

long long int ans = 0;

for(int i=0; i<3; i++){

ans+=dp[N-1][i];

}

cout<<ans<<endl;

cin>>N;

work();

return 0;