#include "bits/stdc++.h"
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
#define printall(n,array) for(int i=0;i<n;i++){cout<<array[i];}cout<<endl;
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
typedef vector<int> VE;
const ll mod = 1000000000;

ll dp[1000003][4];

int main(){
  int n;  cin>>n;
  memset(dp,0,sizeof(dp));
  dp[1][1]=1;
  dp[2][2]=1;
  dp[3][1]=1;
  dp[3][2]=1;
  dp[3][3]=1;
  rep(i,4,n+1){
    dp[i][1]=(dp[i-1][2]+dp[i-1][3])%mod;
    dp[i][2]=(dp[i-2][1]+dp[i-2][3])%mod;
    dp[i][3]=(dp[i-3][2]+dp[i-3][1])%mod;
    //print(1<<":"<<dp[i][1]<<" "<<2<<":"<<dp[i][2]<<" "<<3<<":"<<dp[i][3]);
  }
  print((dp[n][1]+dp[n][2]+dp[n][3])%mod);
}