import java.util.Scanner;
//To calculate Fibonacci Series up to n numbers.
public class Main{
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    //input
    System.out.print("Enter Your Number :");
    int n = in.nextInt();
    // 0 1 1 2 3 5 8 13

    int a = 0;
    int b = 1;
    int count = 2;
    while(count<n){
      int temp = b;
      b = a+b;
      a = temp;
      count++;
    }
    System.out.println(b);
  } 
}