#include <stdio.h>

#define NMAX 10000
#define FIN "litere.in"
#define FOUT "litere.out"

int n,i,j,nr=0;
char v[NMAX];

int main()
{
freopen(FIN,"rt",stdin);
freopen(FOUT,"wt",stdout);

scanf("%d\n", &n);

for (i=1;i<=n;i++)
     scanf("%c",v[i]);

for (i=1;i<n;i++)
    for (j=i+1;j<=n;j++)
	if (v[i]>v[j]) nr++;

printf("%d\n",nr);
return 0;
}