#pragma GCC target("avx512f,avx512dq,avx512cd,avx512bw,avx512vl")
#pragma GCC optimize("O3")
#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int n = ri();
	std::string s;
	std::cin >> s;
	int64_t res = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < i; j++) {
			if (s[i] == s[j]) continue;
			for (int k = 0; k < j; k++) if (j - k != i - j && s[k] != s[i] && s[k] != s[j]) res++;
		}
	}
	printf("%" PRId64 "\n", res);
	return 0;
}
