#include <fstream.h>
int b[27];
int main ()
{
ifstream f ("litere.in");
ofstream g ("litere.out");
char a;
int i;
long c=0;
f>>i;
while (f>>a)
{
b[a-'a']++;
for (i=a-'a'+1;i<=26; i++) c+=b[i];
}
g<<c<<'\n';

return 0;

}