include<bits/stdc++.h>

using namespace std; int main(){

//freopen("10.in","r",stdin);
//freopen("10.out","w",stdout);

long long n,i,a,b,c,d;
cin>>n;
if(n==1){
	cout<<0;
}
else if(n==2 || n==3){
	cout<<1;
}
else {
	a=1; b=1; c=0;
	for(i=4;i<=n;i++){
		d=a+2*b+3*c;
		c=b;
		b=a;
		a=d;
	}
	cout<<d;
	
}
return 0;

}