#include <cstdio>

const int Nmax = 10005;

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

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

	scanf("%d", &N);
	for (int i = 0; i < N; ++i)
		scanf(" %c ", s+i);
}

void Solve() {
	char ok = 1;
	while (ok) {
		ok = 0;
		for (int i = 1; i < N; ++i)
			if (s[i] < s[i-1]) {
				s[i] ^= s[i-1] ^= s[i] ^= s[i-1];
				ok = 1;
				++Ret;
			}
	}
	printf("%d\n", Ret);
}

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