Giải bài trực tuyến

In this problem, you have to multiply two n-bit binary numbers in 2s complement form. The result should be also a n-bit binary number in 2s complement form. In case there is an arithmetic overflow, you program should be able to detect it.

For your information, the 2s complement form of -x is the number 2^n-x. A n-bit 2s complement number ranges from -2^n-1 to 2^n-1-1.

Input

There are multiple test cases (no more than 40). For each test case, there are three input lines. The first line contains n (0 ≤ n ≤ 1024). n=0 signals the end of the input. Otherwise, the second and third lines contain the two n-bit binary numbers.

Output

For each test case, output "overflow" if there is an arithmetic overflow. Otherwise, print the result in 2s complement form.

Example

Input
3
110
011
4
0011
1110
0

Output
overflow
1010