#include<bits/stdc++.h>
#define fi first
#define se second
#define MULT_TEST 1
using namespace std;
typedef long double ldb;
typedef unsigned long long ull;
const int INF = 0x3f3f3f3f;
const int MOD = 998244353;
const int N = 1000006;
char s[N], t[N];
int a[N];
inline int read() {
    int w = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        w = (w << 1) + (w << 3) + ch - 48;
        ch = getchar();
    }
    return w * f;
}
inline void Solve() {
    int n, cnt = 0;
    n = read();
    scanf("%s%s", s + 1, t + 1);
    a[0] = a[n + 1] = 0;
    for (int i = 1; i <= n; i++) a[i] = (s[i] != t[i]);
    for (int i = 1; i <= n + 1; i++) cnt += (a[i] != a[i - 1]);
    if (cnt > 4) printf("0\n");
    else if (cnt == 4) printf("6\n");
    else printf("%d\n", 2 * (n - 1));
}
signed main() {
    int _ = 1;
#if MULT_TEST
    _ = read();
#endif 
    while (_--) Solve();
    return 0;
}