https://www.acmicpc.net/problem/2748
시간 1초, 메모리 128MB
input :
output :
import sys
n = int(sys.stdin.readline())
previous = 0
current = 1
if n == 0:
print(0)
elif n == 1:
print(1)
else:
for i in range(2, n + 1):
temp = current
current += previous
previous = temp
print(current)