def fib(N):
    if N == 1:
        return 1
        
    l = [1, 1] #fib[i-2], fib[i-1]
    
    for i in range(N-1):
        l.append(l[0] + l[1])
       
        l.pop(0)
        
    return l[1]

N = int(input())
print(fib(N))