There are N+1 towns. The i-th town is being attacked by A_i monsters.
We have N heroes. The i-th hero can defeat monsters attacking the i-th or (i+1)-th town, for a total of at most B_i monsters.
What is the maximum total number of monsters the heroes can cooperate to defeat?

-----Constraints-----
- All values in input are integers.
- $1 \leq N \leq 10^5$
- $1 \leq A_i \leq 10^9$
- $1 \leq B_i \leq 10^9$

-----Input-----
Input is given from Standard Input in the following format:
N
A_1 A_2 ... A_{N+1}
B_1 B_2 ... B_N

-----Output-----
Print the maximum total number of monsters the heroes can defeat.

-----Sample Input-----
2
3 5 2
4 5

-----Sample Output-----
9

If the heroes choose the monsters to defeat as follows, they can defeat nine monsters in total, which is the maximum result.
- The first hero defeats two monsters attacking the first town and two monsters attacking the second town.
- The second hero defeats three monsters attacking the second town and two monsters attacking the third town.

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