#include<fstream.h>
int a[10001],s;
int main()
{
	ifstream fin("litere.in");
	ofstream fout("litere.out");
	int i,n,x,t=1;
	char c;
	fin>>n;
	for(i=1;i<=n;i++)
	{
		fin>>c;
		a[i]=int(c);
	}
	while(t!=0)
	{t=0;
		for(i=1;i<n;i++)
		{
			
			if(a[i]>a[i+1])
			{
				x=a[i]; a[i]=a[i+1]; a[i+1]=x;
				s++; t++;
			}
		}
	}
	fout<<s;
	fin.close();
	fout.close();
	return 0;
}