num = 100
DP = [None] * (num+1)
DP[0] = 1
DP[1] = 1

def fib(n):
    for i in range(2, n + 1):
        DP[i] = DP[i-1] + DP[i-2]
        
    return DP[n]

n = int(input())
print(fib(n))