#!/usr/bin/env python3

# Challenge 112
#
# TASK #2 - Climb Stairs
# Submitted by: Mohammad S Anwar
# You are given $n steps to climb
#
# Write a script to find out the distinct ways to climb to the top. You are
# allowed to climb either 1 or 2 steps at a time.
#
# Example
# Input: $n = 3
# Output: 3
#
#     Option 1: 1 step + 1 step + 1 step
#     Option 2: 1 step + 2 steps
#     Option 3: 2 steps + 1 step
#
# Input: $n = 4
# Output: 5
#
#     Option 1: 1 step + 1 step + 1 step + 1 step
#     Option 2: 1 step + 1 step + 2 steps
#     Option 3: 2 steps + 1 step + 1 step
#     Option 4: 1 step + 2 steps + 1 step
#     Option 5: 2 steps + 2 steps

import sys

def count(n):
    if n <= 0:
        return 0
    elif 1 <= n <= 2:
        return n
    else:
        return count(n-1)+count(n-2)

print(count(int(sys.argv[1])))