#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long int
const int MOD = 1000000007;
const int MOD2 = 998244353;
const int INF = LLONG_MAX / 2;
const int MAXN = 100000;
int primes[1000000];
/*void seive() {
fill(primes, primes + 1000000, 1);
primes[0] = primes[1] = 0;
for (int i = 2; i * i < 1000000; i++) {
if (primes[i]) {
for (int j = i * i; j < 1000000; j += i) {
primes[j] = 0;
}
}
}
}
bool isPrime(int n) {
if (n <= 1) return false;
for (int i = 2; i * i <= n; i++) {
if (n % i == 0) return false;
}
return true;
}
int gcd(int a, int b) {
if (a == 0) return b;
return gcd(b % a, a);
}*/
int power(int a, int b, int mod) {
int res = 1;
a %= mod;
while (b > 0) {
if (b & 1) res = res * a % mod;
a = a * a % mod;
b >>= 1;
}
return res;
}
// nCr % MOD for n < MOD
int nCrModP(int n, int r) {
if (r > n) return 0;
if (r == 0 || r == n) return 1;
int numerator = 1, denominator = 1;
for (int i = 0; i < r; i++) {
numerator = (numerator * (n - i)) % MOD;
denominator = (denominator * (i + 1)) % MOD;
}
return (numerator * power(denominator, MOD - 2, MOD)) % MOD;
}
// Lucas's Theorem
int lucas(int n, int r) {
if (r == 0) return 1;
return (lucas(n / MOD, r / MOD) * nCrModP(n % MOD, r % MOD)) % MOD;
}
void solve() {
int n,q;
cin>>n>>q;
string str1,str2;
cin>>str1>>str2;
vector<int>a,b;
for(int i = 0 ; i<n ; i++){
a.push_back(str1[i]-'0');
}
for(int i = 0 ; i<n ; i++){
b.push_back(str2[i]-'0');
}
vector<int>prefixones(n,-1),suffones(n,-1);
int j = 0;
int cnt = 0;
for(int i = 0 ; i<n ; i++){
if(a[i]==1){
cnt += (i-j);
prefixones[j] = cnt;
j++;
}
}
j = n-1;
cnt = 0;
for(int i = n-1 ; i>=0 ; i--){
if(b[i]==1){
cnt += (j-i);
suffones[j] = cnt;
j--;
}
}
int mini = INF;
for(int i = 0 ; i<n ; i++){
if(prefixones[i]!=-1 && suffones[i]!=-1){
mini = min(mini,(prefixones[i]+suffones[i]));
}
}
cout<<((mini!=INF)?mini:-1)<<endl;
}
signed main() {
ios::sync_with_stdio(false); cin.tie(NULL);
int t;
cin >> t;
while (t--) {
solve();
}
return 0;
}
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