python3题解 | #最小花费爬楼梯#

# import sys

# for line in sys.stdin:
#     a = line.split()
#     print(int(a[0]) + int(a[1]))
n = int(input())
cost = []
cost = list(map(int,input().split()))
if not cost:print(None)
res = [0]*(n+1) 
if n == 1:
    print(cost[0])
for i in range(2,n+1):
    res[i] = min(res[i-2]+cost[i-2],res[i-1]+cost[i-1])
print(res[-1])