import java.util.*;
/**
* HJ37 统计每个月兔子的总数 - 简单
*/
public class HJ037 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
while (sc.hasNext()) {
int n = sc.nextInt();
System.out.println(f1(n));
}
sc.close();
}
private static int f(int n) {
if (n == 1 || n == 2) {
return 1;
}
return f(n - 1) + f(n - 2);
}
private static int f1(int month) {
List<Rabbit> rabbitList = new ArrayList<>();
Rabbit rabbit = new Rabbit(1);
rabbitList.add(rabbit);
for (int i = 2; i <= month; i++) {
int birthRabbitCount = 0;// 每个月出生的兔子个数
for (int j = 0; j < rabbitList.size(); j++) {
Rabbit rabbitCurrent = rabbitList.get(j);
rabbitCurrent.month = rabbitCurrent.month + 1; // 每只兔子会成长一个月
if (rabbitCurrent.month > 2) {
birthRabbitCount++;
}
}
// 把每个月出生的兔子加到集合
for (int j = 0; j < birthRabbitCount; j++) {
Rabbit birthRabbit = new Rabbit(1);
rabbitList.add(birthRabbit);
}
}
return rabbitList.size();
}
public static class Rabbit {
public int month;
public Rabbit(int month) {
this.month = month;
}
}
}