import sys
def sum(x, y):
sum = x + y
return sum
def main():
list = [0 for i in range(10001)] # 배열 선언
n = int(input())
list[0] = 0
list[1] = 1
for i in range(2, 10001):
list[i] = sum(list[i-2], list[i-1]) # 다이나믹 프로그래밍
print(list[n])
if __name__ == '__main__':
main()