#include <bits/stdc++.h>

using namespace std;

int main(){
    cin.tie(NULL)->sync_with_stdio(false);

    int n;
    cin >> n;

    string s;
    cin >> s;

    int minWhite = 2 * n - 1;
    int white = 0;
    queue<char> wines;

    for(int i = 0; i < n; i++){
        wines.push(s[i]);

        if(s[i] == 'W')
            white++;
    }

    minWhite = white;

    for(int i = n; i < 2 * n - 1; i++){
        wines.push(s[i]);

        if(s[i] == 'W')
            white++;

        if(wines.front() == 'W')
            white--;

        wines.pop();

        minWhite = min(minWhite, white);
    }

    cout << minWhite << "\n";
}