Problem:
Score : 400 points

Problem Statement

We have a string S of length N consisting of R, G, and B.

Find the number of triples (i,~j,~k)~(1 \leq i < j < k \leq N) that satisfy both of the following conditions:

S_i \neq S_j, S_i \neq S_k, and S_j \neq S_k.

j - i \neq k - j.

Constraints

1 \leq N \leq 4000

S is a string of length N consisting of R, G, and B.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of triplets in question.

Sample Input 1

4
RRGB

Sample Output 1

1

Only the triplet (1,~3,~4) satisfies both conditions. The triplet (2,~3,~4) satisfies the first condition but not the second, so it does not count.

Sample Input 2

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Sample Output 2

1800

Solution in JavaScript (Node.js 12.16.1) (judge verdict: Time Limit Exceeded)

process.stdin.resume();
process.stdin.setEncoding('utf8');

const lines = [];
const reader = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
});
reader.on('line', (line) => {
  lines.push(line)
});
reader.on('close', () => {
  const inputLength = Number(lines[0])
  const inputString = lines[1]
  const inputArray = inputString.split('')
  const rArray = inputArray.filter(element => element === 'R')
  const gArray = inputArray.filter(element => element === 'G')
  const bArray = inputArray.filter(element => element === 'B')

  let sum = 0
  for (let i = 1; i < Number(inputLength) + 1; i++) {
    for (let j = i + 1; j < Number(inputLength) + 1; j++) {
      for (let k = j + 1; k < Number(inputLength) + 1; k++) {
        if(j - i === k - j && inputArray[i - 1] !== inputArray[j - 1]  && inputArray[j - 1] !== inputArray[k - 1] && inputArray[i - 1] !== inputArray[k - 1]){
          sum = sum + 1
        }
      }
    }
  }

  console.log(rArray.length * gArray.length * bArray.length - sum)

});