UVa 514 - Rails

#include<iostream>
#include<stack>
#define MAXN 1005
using namespace std;

int main() {
int N;
while(cin >> N&& N) {
while(1) {
int A = 1, B = 1, Sta[MAXN];
bool ok = true;
stack<int> C;
for(int i = 1; i <= N; i++) {
cin >> Sta[i];
if(!Sta[i]) break;
}
if(!Sta[1]) break;
while(B <= N) {
if(A == Sta[B]) {A++; B++;}
else if(!C.empty()&& C.top() == Sta[B]) {C.pop(); B++;}
else if(A <= N) {C.push(A); A++;}
else {
ok = false;
break;
}
}
ok ? cout << "Yes" << endl : cout << "No" << endl;
}
cout << endl;
}
return 0;
}