for (int i=0; i < a.size(); i++) {
  for (int j=0; j < b.size(); j++) {
    if (a[i]==b[j]) {counter++;}
  }

for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (b[j] >= a[i]) {
        counter++;
        for (int k = i + 1; k < n; k++) {
          if (a[k] >= b[j+1]) {
            counter++;
            for (int l = k + 1; l < m; l++) {
              if (b[l] >= a[k]) {
                counter++;
                ....
              }
            }
          }
        }
      }
    }
  }