http://acm.csu.edu.cn/OnlineJudge/showsource.php?id=97625
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
int a[200000];
int main()
{
int n,m;
int i,j,k;
while(scanf("%d%d",&n,&m)!=EOF)
{
int t1;
char t2[1000];
for(i=0;i<n;i++)
scanf("%d%s",&t1,t2);
int l=n/3;
int r=n-n/3+1;
if(n%3==2) r--;
if(m>l&&m<r) printf("YES\n");
else printf("NO\n");
}
return 0;
}