PAT乙级1007素数对猜想（20）

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cmath>
 4 using namespace std;
 5 int judge(int n){
 6     int k = (int)sqrt(1.0*n);
 7     if(n<=1)
 8     return 0;
 9     for(int i = 2;i<=k;i++){
10         if(n%i==0)
11         return 0;
12     }
13     return 1;
14 }
15 int main(){
16     int n;
17     scanf("%d",&n);
18     int count = 0;
19     for(int i = 3;i<=n;i+=2){
20         if(judge(i)==1&&judge(i-2)==1)
21         count++;
22     }
23     printf("%d",count);
24     return 0;
25 }