Code Forces 26A Almost Prime

D - Almost Prime
Time Limit:2000MS Memory Limit:262144KB 64bit IO Format:%I64d & %I64u
SubmitStatusPracticeCodeForces
26A

Description

A number is called almost prime if it has exactly two distinct prime divisors. For example, numbers 6, 18, 24 are almost prime, while 4, 8, 9, 42 are not. Find the amount of almost prime numbers which are between 1 andn,
inclusive.

Input

Input contains one integer number n (1 ≤ n ≤ 3000).

Output

Output the amount of almost prime numbers between 1 and
n, inclusive.

Sample Input

Input

10

Output

2

Input

21

Output

8

水题。开个数组记录个数。

#include <stdio.h>
#include <string.h>
int flag[3005];
int main()
{
memset(flag,0,sizeof(flag));
int n;
scanf("%d",&n);
int sum=0;
for(int i=2;i<=n;i++)
{
for(int j=2;j<i;j++)
if(i%j==0&&flag[j]==0)
flag[i]++;
if(flag[i]==2)
sum++;
}
printf("%d\n",sum);
}