시간 제한 메모리 제한 제출 정답 맞은 사람 정답 비율
2 초 512 MB 2 2 2 100.000%

## 문제

You are given three distinct binary vectors of length n. Find any 2-CNF formula which satisfies the following conditions:

• The formula is true on these vectors;
• The number of vectors on which the formula is true is minimal possible;
• The formula is not too long.

Recall that a 2-CNF formula is a propositional formula of n boolean variables v1, . . . , vn which looks like

C1 ∧ C2 ∧ . . . ∧ Cm,

where each clause Ci is represented as a disjunction ±xi1 ∨ ±xi2 of two literals (by literal, we mean any variable or its negation). Here, xij ∈ {v1, . . . , vn} is one of the variables, and −xij is its negation: true becomes false, and false becomes true. We say that the formula f is true on a binary vector v if f(v1, v2, . . . , vn) = 1.

If there are several valid formulas, you are allowed to output any one of them.

## 입력

The first line of input contains a single integer n which denotes the length of the three vectors (2 ≤ n ≤ 105). The i-th of the following three lines contains a binary string of length n denoting the i-th binary vector.

No two vectors coincide.

## 출력

On the first line, print a single integer m (0 ≤ m ≤ 2 · 105). Then output m lines, i-th of them containing two integers ai and bi (1 ≤ |ai|, |bi| ≤ n), denoting that the i-th clause is a conjunction of two literals: the first is vai if ai > 0 and −v|ai| otherwise, and the second is, similarly, vbi if bi > 0 and −v|bi| otherwise. If your formula is empty (that is, m = 0), it is considered to be true for every possible input vector of size n.

5
00101
10011
11011

6
-1 -3
3 1
-1 4
-4 1
5 5
-2 1

3
100
010
001

3
-2 -1
-3 -1
-3 -2