#include <bits/stdc++.h>
using namespace std;

int main() {
    int left_o, left_l, right_o, right_l, n;
	string s;
	cin >> n >> s;
	for (int i = 1; i <= n - 1; i++) { //遍历字符串的每一位
		left_o = 0, left_l = 0, right_o = 0, right_l = 0; //初始化
		for (int j = 0; j <= i - 1; j++) { //统计前缀
			if (s[j] == 'O') {
				left_o++;
			} else {
				left_l++;
			}
		}
		for (int j = i; j <= n - 1; j++) { //统计后缀
			if (s[j] == 'O') {
				right_o++;
			} else {
				right_l++;
			}
		}
		if (left_o != right_o && left_l != right_l && left_o + left_l > 0 && right_o + right_l > 0) {
            //如果前、后缀字母O和L的数量不等
			cout << i; //输出该位置
			return 0; //结束程序
		}
	}
	cout << -1; //不可能存在答案
	return 0; //完结
}