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