#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5, M = 1e5 + 5;
const long long INF = 1e18 + 5;
inline long long read() {
  long long sum = 0, fh = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') fh = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    sum = sum * 10 + c - '0';
    c = getchar();
  }
  return sum * fh;
}
inline int read2() {
  char c = getchar();
  while (c < '0' || c > '9') {
    c = getchar();
  }
  return c - '0';
}
inline int read3() {
  char c = getchar();
  while (c < 'a' || c > 'z') {
    c = getchar();
  }
  return c - 'a';
}
inline void write(long long x) {
  if (x < 0) putchar('-'), x = -x;
  if (x > 9) write(x / 10);
  putchar(x % 10 + '0');
}
inline int gcd(int x, int y) { return y == 0 ? x : gcd(y, x % y); }
inline long long ab(long long x) { return x < 0 ? -x : x; }
inline long long fpow(long long qwe, long long asd, long long zxc) {
  long long a = qwe, b = 1, c = asd;
  while (c) {
    if (c & 1) b = b * a % zxc;
    a = a * a % zxc;
    c >>= 1;
  }
  return b;
}
int a[N], b[N] = {0};
queue<int> qwe[27];
int c[N] = {0}, n;
inline void add(int x, int k) {
  while (x <= n) {
    c[x] += k;
    x += (x & -x);
  }
}
inline int cx(int x) {
  int sum = 0;
  while (x) {
    sum += c[x];
    x -= (x & -x);
  }
  return sum;
}
int main() {
  n = read();
  for (int i = 1; i <= n; ++i) {
    a[i] = read3();
    b[n - i + 1] = a[i];
    qwe[a[i]].push(i);
  }
  long long ans = 0;
  for (int i = 1; i <= n; ++i) {
    int x = b[i], y = qwe[x].front(), z = cx(y);
    qwe[x].pop();
    ans += y + z - i;
    add(1, 1);
    add(y + 1, -1);
  }
  cout << ans << endl;
}
