# UUID: e5d10dbd-314c-4006-9bed-fcba7ee6ffd4
#n = int(input())
#dij = list(map(int, input().split()))
#op = [0 for i in range(n)]
#
#op[0] = dij[0]
#op[1] = dij[0] + dij[1]
#
#for i in range(2, len(dij)):
#    op[i] = (min(op[i-1], op[i-2]) + dij[i])
#
#print(op[-1])

def solve():
    n = int(input())
    a = [int(x) for x in input().split()]
    dp = [0] * n
    dp[0] = a[0]
    dp[1] = a[0] + a[1]
    for i in range(2, n):
        dp[i] = min(dp[i-1], dp[i-2]) + a[i]
    print(dp[n-1])

solve()