// litere.cpp : Defines the entry point for the console application.
//

#include <stdio.h>
#include <stdlib.h>
char e[10004];
int main()
{
	int i,n,pozlibera=1,schi=0,j,l,temp,temp2,k;
	FILE *f1,*f2;
	f1=fopen("litere.in","r");
	f2=fopen("litere.out","w");
	fscanf(f1,"%d",&n);
	fread(e,10004,1,f1);
	for(i=97;i<=122;i++)
	{
		for(j=pozlibera;j<=n;j++)
		{
			if(e[j]==i)
			{
				k=e[j];
				temp=e[pozlibera];
				for(l=pozlibera+1;l<=j;l++)
				{
					temp2=temp;
					temp=e[l];
					e[l]=temp2;
				}
				e[pozlibera]=k;
				schi=schi+j-pozlibera;
				pozlibera++;
			}
		}
	}
	fprintf(f2,"%d",schi);
	fclose(f1);
	fclose(f2);

	return 0;
}