#include <stdio.h>

int main()
{
	FILE* fin = fopen("litere.in", "r");
	FILE* fout = fopen("litere.out", "w");

	int N;
	fscanf(fin, "%d", &N);

	char sir[10001];

	fscanf(fin, "%s", sir);

	long long int ct = 0;
	for (int i = 1; i < N; i++)
	{
		if (sir[i] < sir[i-1])
		{
			for (int j = i; j >= 1; j--)
			{
				if (sir[j] >= sir[j-1])
					break;
				char aux = sir[j];
				sir[j] = sir[j-1];
				sir[j-1] = aux;

				ct++;
			}
		}
	}

	fprintf(fout, "%lld", ct);

	fclose(fin);
	fclose(fout);

	return 0;
}