import sys
sys.setrecursionlimit(3000)  #using to increase depth of recursion

def fib(n):
    if n==1 or n==2:
        return 1
    fib_n_1=fib(n-1)
    fib_n_2=fib(n-2)
    output=fib_n_1 + fib_n_2
    return output

n=int(input())

print(fib(n))