import sys

def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

def solve():
    n = int(input())

    ans = fib(n)

    print(ans)
    pass

def fib(n):
    if n <= 1:
        return 1
    else:
        f0, f1 = 1, 1

        for i in range(n - 1):
            f1, f0 = f1 + f0, f1

        return f1

if __name__ == '__main__':
    solve()