1 #include <iostream>
 2 using namespace std;
 3 struct Point {
 4     int x,y;
 5 };
 6 int Cross(Point a,Point b,Point c)    //叉积
 7 {
 8     return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
 9 }
10 bool isConvex(Point p[],int n)    //判断多边形是否是凸多边形，必须是按顺序排列的
11 {
12     int i;
13     p[n+1] = p[1];
14     p[n+2] = p[2];    //注意！！每一条边都要遍历
15     for(i=1;i<=n;i++)
16         if(Cross(p[i],p[i+1],p[i+2])>0)    //是否右拐
17             return false;
18     return true;
19 }
20 int main()
21 {
22     int n;
23     while(cin>>n){
24         if(n==0) break;
25         int i;
26         Point p[1010];
27         for(i=1;i<=n;i++)
28             cin>>p[i].x>>p[i].y;
29         if(n<3 || isConvex(p,n))    //判断
30             cout<<"convex"<<endl;
31         else
32             cout<<"concave"<<endl;
33     }
34     return 0;
35 }