poj 1868 Antiarithmetic?

#include<cstdio>#include<algorithm>using namespace std;const int N=10005;int pos[N];int main(){    int n,f;    while(scanf("%d",&n),n)    {        getchar();        for(int i=0,tp;i<n;i++)        { scanf("%d",&tp); pos[tp]=i;        }        f=0;        for(int i=1;!f&&i<n-1;i++) for(int j=1,lim=min(n-1-i,i);!f&&j<=lim;j++)     if((pos[i+j]-pos[i])*(pos[i-j]-pos[i])<0)         f=1;        printf("%sn",f?"no":"yes");    }    return 0;}