import sys

def ex(n):
    if n <= 0: return 0
    if n == 1: return 1
    
    a, b = 0, 1
    for _ in range(2, n + 1):
        a, b = b, a + b
    return b

for s in sys.stdin:
    line = s.strip()
    if not line:
        continue
    n = int(line)
    print(ex(n + 1))