#include<iostream.h>
#include<fstream.h>
ifstream f("litere.in");
ofstream g("litere.out");
int main()
{
int n;
char c[10000];
f>>n;
for(int i=1;i<=n;i++)
	f>>c[i];
f.close();
int flag=1;
long contor=0;
while(flag)
{flag=0;
for(int i=1;i<=n-1;i++)
{
if (c[i+1]<c[i])
	{int aux=c[i];c[i]=c[i+1];c[i+1]=aux;flag=1;contor++;break;}
}
}
g<<contor;
f.close();
g.close();
return 0;
}