import java.util.Scanner;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
public static int getStep(int count) {
if (count == 1) return 1;
if (count == 2) return 2;
return getStep(count - 1) + getStep(count - 2);
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int count = in.nextInt();
int mt1 = 1;
int mt2 = 2;
if (count == 1 || count == 2) {
System.out.println(count);
return ;
}
for (int i = 3; i <= count; i++) {
int temp = mt2;
mt2 = mt1 + mt2;
mt1 = temp;
}
System.out.println(mt2);
// 注意 hasNext 和 hasNextLine 的区别
// while (in.hasNextInt()) { // 注意 while 处理多个 case
// int a = in.nextInt();
// int b = in.nextInt();
// System.out.println(a + b);
// }
}
}