N = int(input())
dp = [0 for _ in range(N+1)]

def rec(i):
    if not dp[i] == 0:
        return dp[i]
    else:
        if i >= 2:
            dp[i] = rec(i-1) + rec(i-2)
        elif i == 1:
            dp[i] = rec(i-1)
        elif i == 0:
            dp[i] = 1
        else:
            raise ValueError("No such value")
        return dp[i]
        
print(rec(N))