import java.util.*; import java.io.*; public class Main { static final int INF = 1<<30; static final long INFL = 1L<<60; static final int MOD = 1000000007; static final int MOD2 = 998244353; static List> g; public static void main(String[] args) { FastScanner fs = new FastScanner(); int n = fs.nextInt(); long[] dp = new long[n+1]; dp[0] = 1; for(int i = 0; i < n; i++){ if(i+2 <= n) dp[i+2] += dp[i]; dp[i+1] += dp[i]; } PrintWriter pw = new PrintWriter(System.out); pw.println(dp[n]); pw.close(); } } class Util{ static void print(int[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } static void print(long[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } static void print(char[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } static void print(double[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } static void print(Integer[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } static void print(Long[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } static void print(String[] arr) { System.out.print("["); for(int i = 0; i < arr.length; i++){ if(i == arr.length-1) System.out.println(arr[i] + "]"); else System.out.print(arr[i] + ", "); } } } class FastScanner { private InputStream in = System.in; private byte[] buffer = new byte[1024]; private int length = 0, p = 0; private boolean hasNextByte() { if (p < length) return true; else{ p = 0; try{ length = in.read(buffer); }catch(Exception e){ e.printStackTrace(); } if(length == 0) return false; } return true; } private int readByte() { if (hasNextByte() == true) return buffer[p++]; return -1; } private static boolean isPrintable(int n) { return 33 <= n && n <= 126; } private void skip() { while (hasNextByte() && !isPrintable(buffer[p])) p++; } public boolean hasNext() { skip(); return hasNextByte(); } public String next() { if(!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int temp = readByte(); while (isPrintable(temp)) { sb.appendCodePoint(temp); temp = readByte(); } return sb.toString(); } public int nextInt() { return Math.toIntExact(nextLong()); } public int[] nextInts(int n) { int[] ar = new int[n]; for (int i = 0; i < n; i++) ar[i] = nextInt(); return ar; } public long[] nextLongs(int n) { long[] ar = new long[n]; for (int i = 0; i < n; i++) ar[i] = nextLong(); return ar; } public long nextLong() { if(!hasNext()) throw new NoSuchElementException(); boolean minus = false; int temp = readByte(); if (temp == '-') { minus = true; temp = readByte(); } if (temp < '0' || '9' < temp) throw new NumberFormatException(); long n = 0; while (isPrintable(temp)) { if ('0' <= temp && temp <= '9') { n *= 10; n += temp - '0'; } temp = readByte(); } return minus ? -n : n; } }