#include <iostream>
#include <cstdio>
#include <cmath>
#include <sstream>
#include <cstring>
#define int long long
using namespace std;

const int N = 1e6 + 100;
int t;
int n , x , num[N];
char c1[N] , c2[N];

signed main() {
	cin >> t;
	while(t --) {
		cin >> n;
		cin >> c1 + 1 >> c2 + 1;
		num[0] = 0;
		for(int i = 1;i <= n;i ++) {
			if(c1[i] == c2[i]) num[i] = 0;
				else num[i] = num[i - 1] + 1;
		}
		int sum = 0;
		int k1 = 0 , k2 = 0;
		num[n + 1] = 0;
		for(int i = 2;i <= n + 1;i ++) {
			if(num[i] == 0 && num[i - 1] > 0) {
				sum ++;
				if(k1 != 0) k2 = num[i - 1];
					else k1 = num[i - 1];
			}
		}
		if(sum > 2) cout << 0 << endl;
			else if(sum == 2) cout << 6 << endl;
				else if(sum == 0) cout << n << endl;
					else cout << (k1 - 1) * 2 << endl;
					
	}
	return 0;
}