11 podryad

#include <iostream>

using namespace std;

int main(){
    int n;
    cin>>n;

    if(n==1){
        cout<<3;
        return 0;
    }
    else if(n==2){
        cout<<8;
        return 0;
    }


    int k00=1, k01=1, k02=1;
    int k10=1, k12=1;
    int k20=1, k21=1, k22=1;

    for(int i=3;i<=n;i++){
        int kk00=k00+k10+k20;
        int kk01=k00+k10+k20;
        int kk02=k00+k10+k20;
        int kk10=k01+k21;
        int kk12=k01+k21;
        int kk20=k02+k12+k22;
        int kk21=k02+k12+k22;
        int kk22=k02+k12+k22;

        k00=kk00;
        k01=kk01;
        k02=kk02;
        k10=kk10;
        k12=kk12;
        k20=kk20;
        k21=kk21;
        k22=kk22;
    }
    cout<<k00+k01+k02+k10+k12+k20+k21+k22;
}