#include <cstdio>
#include <cassert>

const int Nmax = 10005;
const int Sigma = 26;

int N;
char s[Nmax];
int Frecventa[Sigma];
int Ret;

void ReadData() {
	freopen("litere.in", "r", stdin);
	freopen("litere.out", "w", stdout);

	scanf("%d", &N);
	assert(1 <= N && N <= 10000);
	for (int i = 0; i < N; ++i) {
		scanf(" %c ", s+i);
		assert('a' <= s[i] && s[i] <= 'z');
	}
}

void Solve() {
	for (int i = 0; i < N; ++i) {
		for (int j = s[i]-'a'+1; j < 26; ++j)
			Ret += Frecventa[j];
		++Frecventa[s[i]-'a'];
	}
	printf("%d\n", Ret);
}

int main() {
	ReadData();
	Solve();
	return 0;
}