@ExperimentalStdlibApi
fun main(args: Array<String>) = abc162d()

@ExperimentalStdlibApi
fun abc162d() {
    val n = readLine()!!.toInt()
    val s = readLine()!!

    val csRed = s.scan(0) { acc, c -> acc + if (c == 'R') 1 else 0 }.toIntArray()
    val csGreen = s.scan(0) { acc, c -> acc + if (c == 'G') 1 else 0 }.toIntArray()
    val csBlue = s.scan(0) { acc, c -> acc + if (c == 'B') 1 else 0 }.toIntArray()

    val list = listOf(csRed, csGreen, csBlue)

    var answer = 0L

    for (i in 0 until n) {
        val c = s[i]
        val other = when (c) {
            'R' -> list - csRed
            'G' -> list - csGreen
            else -> list - csBlue
        }
        for (j in i + 1 until n) {
            val c2 = s[j]
            if (c2 == c) continue
            val remain = when (c2) {
                'R' -> other - csRed
                'G' -> other - csGreen
                else -> other - csBlue
            }[0]

            val jump = j + (j - i) + 1

            answer += remain.last() - remain[j] -
                    if (jump in remain.indices) remain[jump] - remain[jump - 1] else 0
        }
    }

    println(answer)
}
