# 这个勾八题不好理解
slong=int(input())
s=input().split()
s=[int(i) for i in s]+[0]
dp=[0,0]
for i in range(2,slong+1):
    dp.append(min(dp[i-1]+s[i-1],dp[i-2]+s[i-2]))
print(dp[slong])