AOJ 9.University

打表
 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <cstring>
 4 #include <cmath>
 5 using namespace std;
 6 
 7 #define REP(n) for(int o=0;o<n;o++)
 8 
 9 const int maxn = 10000005;
10 bool is_prime[maxn];
11 int prime_cnt[maxn];
12 
13 void prime() {
14     memset(is_prime,true,sizeof(is_prime));
15     int len = (int)sqrt(maxn + 0.5);
16     for(int i = 2;i <= len;i++)
17         if(is_prime[i])
18             for(int j = i*i;j < maxn;j += i)
19                 is_prime[j] = false;
20     is_prime[1] = false;
21 
22 
23     prime_cnt[0] = 0;
24     for(int i = 1;i < maxn;i++)
25         prime_cnt[i] = prime_cnt[i - 1] + is_prime[i];
26 }
27 
28 int main() {
29     prime();
30 
31     int n;
32     while(scanf("%d",&n), n!= 0) {
33         printf("%d
",prime_cnt[n]);
34     }
35 
36     return 0;
37 }