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


string s;
int n;
int f[1000005], g[1000005];

int main()
{
	ios::sync_with_stdio(false);
	cin >> n >> s;

	f[0] = g[0] = 0;

	for(int i=0; i<n; i++) {
		if(s[i] == 'A') {
			f[i+1] = f[i];
			g[i+1] = 1 + min( f[i], g[i] );
		}
		else {
			g[i+1] = g[i];
			f[i+1] = 1 + min( f[i], g[i] );
		}
    }
	printf("%d\n", f[n]);
}