#include <bits/stdc++.h>
using namespace std;
string s[2];
int comp[2][1000000];
int vis[2][1000000];
int n;
void dfs(int i, int j, int col) {
  if (i >= 2 || j >= n || i < 0 || j < 0) return;
  if (s[i][j] == 'X') return;
  if (vis[i][j]) return;
  vis[i][j] = 1;
  comp[i][j] = col;
  dfs(i + 1, j, col);
  dfs(i, j + 1, col);
  dfs(i, j - 1, col);
  dfs(i - 1, j, col);
}
int L[1000000];
int R[1000000];
int sum[1000000];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int q;
  cin >> n >> q;
  int V = 0;
  cin >> s[0] >> s[1];
  for (int i = 0; i < 2; i++) {
    for (int j = 0; j < n; j++) {
      if (!vis[i][j]) dfs(i, j, ++V);
    }
  }
  if ((s[0][0] == 'X') + (s[1][0] == 'X') == 1)
    L[0] = 0;
  else
    L[0] = -1;
  if ((s[0].back() == 'X') + (s[1].back() == 'X') == 1)
    R[n - 1] = n - 1;
  else
    R[n - 1] = n + 1;
  for (int i = 1; i < n; i++) {
    L[i] = L[i - 1];
    if ((s[0][i] == 'X') + (s[1][i] == 'X') == 1) L[i] = i;
  }
  for (int i = n - 2; i >= 0; i--) {
    R[i] = R[i + 1];
    if ((s[0][i] == 'X') + (s[1][i] == 'X') == 1) R[i] = i;
  }
  for (int i = 0; i < n; i++) {
    if (i) sum[i] = sum[i - 1];
    if (i && L[i] == i && L[i - 1] != -1 && s[0][L[i - 1]] != s[0][i]) sum[i]++;
  }
  while (q--) {
    int x, y;
    cin >> x >> y;
    int x1 = (x - 1) / n;
    int y1 = (x - 1) % n;
    int x2 = (y - 1) / n;
    int y2 = (y - 1) % n;
    x = y1;
    y = y2;
    if (y1 > y2) {
      swap(y1, y2);
      swap(x1, x2);
      swap(x, y);
    }
    if (comp[x1][y1] != comp[x2][y2]) {
      cout << "-1\n";
    } else {
      if (R[x] > L[y])
        cout << y - x + abs(x1 - x2) << endl;
      else {
        int add = 0;
        if (x1 == 0 && s[0][R[x]] == 'X') add++;
        if (x1 == 1 && s[1][R[x]] == 'X') add++;
        if (x2 == 0 && s[0][L[y]] == 'X') add++;
        if (x2 == 1 && s[1][L[y]] == 'X') add++;
        cout << y - x + sum[L[y]] - sum[R[x]] + add << endl;
      }
    }
  }
}
