C :

# include <stdio.h>
# include <stdlib.h>

int main()
{

    char ch, c;
    long long n;
    long long count;
    while( scanf("%lld%*c", &n) != EOF)
    {
        count = 0;
        ch = getchar();
        n --;
        while( n --)
        {
            c = getchar();
            if( c == ch)
            {
                count ++;
            }
            else
            {
                ch = c;
            }
        }
        getchar();
        printf("%lld\n", count);
    }
    return 0;
}

C++ :

#include<iostream>
using namespace std;

int main()
{
  int n;string s;
  while(cin>>n>>s)
  {
      int ans=0;
      for(int i=1;i<n;i++)
          ans+=s[i]==s[i-1];
        cout<<ans<<endl;
  }}

Java :

import java.util.Scanner;


public class Main {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
        Scanner cin=new Scanner(System.in);
        while(cin.hasNext())
        {
        	int N=cin.nextInt();
        	String str=cin.next();
        	int count=0;
        	for(int i=0;i<N-1;i++)
        	{
        		if(str.charAt(i)==str.charAt(i+1))
        		{
        			count++;
        		}
        	}
        	System.out.println(count);
        }
	}

}