514 - Rails - UVA

#include<cstdio>
#include<stack>
using namespace std;
int main() {
 int n, val;
 while (1) {
  scanf("%d", &n);
  if (n == 0) break;
  while (1) {
   scanf("%d", &val);
   if (val == 0) {
    printf("\n");
    break;
   }
   stack A, B;
   A.push(val);
   for (int i = 1; i < n; i++) {
    scanf("%d", &val);
    A.push(val);
   }
   int i = n;
   for (; i >= 1;) {
    if (!B.empty() && B.top() == i) {
     B.pop();
     i--;
     continue;
    }
    if (A.empty()) break;
    if (A.top() != i) B.push(A.top());
    else i--;
    A.pop();
    
   }
   if (A.empty() && B.empty()) puts("Yes");
   else puts("No");
  }
 }
 return 0;
}