#include <iostream>
#include <cmath>
#include <cstring>
#include <string>
#include <set>
#include <stack>
#include <ctime>
#include <queue>
#include <algorithm>
#define ll long long
#define INF 0x3f3f3f3f
using namespace std;
const int N = 1e6+100;
/*
*/
int n;
char s[110];
int res = INF;
int vis[110];
int memo[110][110];
void dfs(int x, int step) {
	if(memo[x][step] != INF) {
//		printf("(%d,%d)\n", x, step);
		res = memo[x][step];
		return;
	}
	if(x > n-1) return;
	if(x == n-1) {
		res = min(res, step);
		memo[x][step] = res;
		return;
	}
	for(int i = 1; i <= 3; ++i) {
		if(!vis[x+i]) {
			vis[x+i] = 1;
			if(s[x+i] == 'X')
				dfs(x+i, step+1);
			else
				dfs(x+i, step);
			vis[x+i] = 0;
		}
	}
}
int main() {
	ios::sync_with_stdio(false);  cin.tie(0);
	memset(memo, 0x3f, sizeof(memo));
	cin >> n >> s;
	if(s[0] == 'X')
		dfs(0,1);
	else
		dfs(0,0);
	cout << res << endl;
	return 0;
}