#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
inline int read() {
  int s = 0, w = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') w = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    s = s * 10 + ch - '0';
    ch = getchar();
  }
  return s * w;
}
int T, n, m;
int main() {
  T = read();
  while (T--) {
    n = read();
    m = read();
    if (n == 1)
      printf("0\n");
    else if (n == 2)
      printf("%d\n", m);
    else
      printf("%d\n", 2 * m);
  }
  return 0;
}
