#include <iostream>
#include <vector>
#include <cstring>

using namespace std;

int main()
{
    int N = 2;
    int t;
    cin >> t;
    while(t -- )
    {
        int n;
        vector<string> s(N);
        cin >> n;
        for(auto& x : s)
        {
            cin >> x;
        }
        int ans = 0;
        for(int i = 1; i < n - 1; i ++ )
        {
            bool flag = true;
            flag &= (s[0][i] == '.' && s[1][i] == '.');
            flag &= (s[0][i - 1] != s[1][i - 1]);
            flag &= (s[0][i + 1] != s[1][i + 1]);
            flag &= (s[0][i - 1] == s[0][i + 1]);
            ans += flag;
        }

        cout << ans << "\n";
    }

    return 0;
}