#include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };
unsigned char dp[65536][16];
struct st{
	unsigned short haichi;
	unsigned char pos;
};
queue<st> P;
int main() {
	int n;
	while (cin >> n,n){
		string s, ans_s;
		cin >> s;
		cin >> ans_s;
		unsigned short sh=0;
		unsigned short ans_sh=0;
		REP(i, n){
			sh <<= 1;
			ans_sh <<= 1;
			if (s[i] == 'W')
				sh |= 1;
			if (ans_s[i] == 'W')
				ans_sh |= 1;
		}
		REP(i, 65536 * 16)
			dp[i / 16][i % 16] = 255;
		
		REP(i, n){
			P.push({ sh, (unsigned char)i });
			dp[sh][i] = 0;
		}
	
		while (!P.empty()){
			st p = P.front(); P.pop();
			unsigned short diff=p.haichi^ans_sh;
			vector<unsigned char> db;
			vector<unsigned char> dw;
			REP (i,n){
				if ((diff >> i) & 1)
					if (!((p.haichi >> i) & 1))
						db.push_back(i);
					else
						dw.push_back(i);
			}
			REP(i, db.size()){
				REP(j,dw.size()){
					unsigned short change = (1 << db[i]) + (1 << dw[j]);
					change ^= p.haichi;
					if (dp[change][db[i]]>dp[p.haichi][p.pos]+abs(p.pos - dw[j]) + abs(db[i] - dw[j])){
						dp[change][db[i]] = dp[p.haichi][p.pos] + abs(p.pos - dw[j]) + abs(db[i] - dw[j]);
						P.push({ change, db[i] });
					}
					if (dp[change][dw[j]]>dp[p.haichi][p.pos] + abs(p.pos - db[i]) + abs(db[i] - dw[j])){
						dp[change][dw[j]] = dp[p.haichi][p.pos] + abs(p.pos - db[i]) + abs(db[i] - dw[j]);
						P.push({ change, dw[j] });
					}
				}
			}
		}
		int min_ans=255;
		REP(i,n){
			min_ans = min((int)dp[ans_sh][i],min_ans);
		}
		cout << min_ans << endl;
	}
}