def sugoroku(x):
    s = [0 for i in range(x+1)]
    s[0] = 1
    s[1] = 1
    for i in range(x-1):
        s[i+2] = s[i+1] + s[i]
    return s[-1]

if __name__ == "__main__":
    print(sugoroku(int(input())))