/* -*- coding: utf-8 -*-
 *
 * 1924.cc:  No.1924 3 color painting on a line - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int MAX_N = 100000;
const char ps[] = "RGB";
const int INF = 1 << 30;

/* typedef */

/* global variables */

char s[MAX_N + 4];

/* subroutines */

int check(int l, int r) {
  int c = 0;
  for (int i = l; i < r;) {
    int j = i;
    while (i < r && s[j] == s[i]) i++;
    c++;
  }
  return c / 2 + 1;
}

/* main */

int main() {
  int n;
  scanf("%d%s", &n, s);

  int mind = INF;
  for (int ci = 0; ci < 3; ci++) {
    char p0 = ps[ci];
    int d = 1;
    for (int i = 0; i < n;) {
      while (i < n && s[i] == p0) i++;
      if (i >= n) break;
      int j = i;
      while (i < n && s[i] != p0) i++;
      d += check(j, i);
    }

    mind = min(mind, d);
  }

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