import java.io.*;
public class Main {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String s = br.readLine();
int n = Integer.parseInt(s);
int dp[] = new int [n+1];
dp[1]=1;
dp[0]=1;
for(int i=2; i<n+1; i++){
dp[i]=dp[i-1]+dp[i-2];
}
System.out.println(dp[n]);
}
}