import java.util.Scanner;

/**
 * yukicoder no.44
 * @author scache
 *
 */
public class DpSugoroku {
	public static void main(String[] args) {
		DpSugoroku p = new DpSugoroku();
	}

	public DpSugoroku() {
		Scanner sc = new Scanner(System.in);
		int n =sc.nextInt();
		
		solve(n);
	}

	public void solve(int n) {
		long[] dp = new long[n+2];
		
		dp[0] = 1;
		for(int i=0;i<dp.length-2;i++){
			dp[i+1] += dp[i];
			dp[i+2] += dp[i];
		}
		
		System.out.println(dp[n]);
	}

}