n=int(input())
L=list(map(int,input().split()))
l=list(map(int,input().split()))
s=0
for i in range(n):
    if L[i]+L[i+1]<=l[i]:
        s+=L[i]+L[i+1]
    elif L[i]<l[i] and L[i]+L[i+1]>l[i]:
        L[i+1]-=l[i]-L[i]
        s+=l[i]
    else:
        s+=l[i]
print(s)有老哥帮忙看下第二题代码哪错了吗，实在想不通为啥是0