#include <iostream>
#include <string>
using namespace std;

int maxConsecutiveOnes(string s) {
    int count = 0;
    int maxCount = 0;
    
    for (char c : s) {
        if (c == '1') {
            count++;
        } else {
            maxCount = max(maxCount, count);
            count = 0;
        }
    }
    maxCount = max(maxCount, count);
    
    return maxCount;
}

int main() {
    int T;
    cin >> T;
    while (T--) {
        int N;
        cin >> N;
        string S;
        cin >> S;
        
        int totalOnes = 0;
        for (char c : S) {
            if (c == '1') totalOnes++;
        }

        if (totalOnes == 0) {
            cout << 0 << endl;
            continue;
        }

        int totalFlips = N - totalOnes;

        if (totalFlips >= 1) {
            cout << totalOnes + min(totalFlips, totalOnes) << endl;
        } else {
            cout << totalOnes << endl;
        }
    }
    return 0;
}