# The Fibonacci sequence

def fibonacci(n):
    if n < 0:
        return -1
    if n == 0:
        return 0
    if n == 1:
        return 1

    # For n >= 2
    prev2 = 0  # F(n-2)
    prev1 = 1  # F(n-1)
    for i in range(2, n + 1):
        current = prev1 + prev2
        # Shift values for next iteration
        prev2 = prev1
        prev1 = current
    return prev1


if __name__ == '__main__':
    start_num = int(input())
    print(f'fibonacci({start_num}) is {fibonacci(start_num)}')