ABC135 C - City Savers에서 배운

N = int(input())

A = list(map(int,input().split()))
B = list(map(int,input().split()))

score = 0
marg = 0
for i in range(N):
    num = A[i]-marg
    if num > 0:
        score += marg
        A[i] -= marg
        if B[i] >= A[i]:
            score += A[i]
            marg = B[i]-A[i]
        else:
            score += B[i]
            marg = 0 # <= ここを忘れて WA (泣)
    else:
        score += A[i]
        marg = B[i]

if A[-1]-marg >= 0:
    score += marg
else:
    score += A[-1]
print(score)#123ms

N = int(input())
A = list(map(int,input().split()))
B = list(map(int,input().split()))

sup = 0
cnt = 0
for i in range(N):
    a,b = A[i],B[i]
    if a <= b:
        cnt += a
        if A[i+1] >= b-a:
            A[i+1] -= b-a
            cnt += b-a
        else:
            cnt += A[i+1]
            A[i+1] = 0
    else:
        cnt += b
print(cnt)#119ms