A. Almost Prime

A. Almost Prime

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

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 and n, 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 test(s)

input

10

output

2

input

21

output

8

/* ***********************************************
Author        :
Created Time  :2015/6/12 14:48:26
File Name     :7.cpp
************************************************ */
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <iomanip>
#include <list>
#include <deque>
#include <stack>
#define ull unsigned long long
#define ll long long
#define mod 90001
#define INF 1<<30
#define maxn 3000+10
#define cle(a) memset(a,0,sizeof(a))
const ull inf = 1LL << 61;
const double eps=1e-5;
using namespace std;

bool cmp(int a,int b){
    return a>b;
}
int used[maxn];
int f[maxn];
void Set(){
cle(f);
memset(used,1,sizeof(used));
for(int i=2;i<=maxn/2;i++){
if(used[i]){
used[i]=0;
for(int j=i+i;j<maxn;j+=i){
f[j]++;
used[j]=0;
}
}
}/*
for(int i=4;i<=40;i++){
cout<<f[i]<<" ";
if(i%7==0)cout<<endl;
}*/
}
int main()
{
    #ifndef ONLINE_JUDGE
    //freopen("in.txt","r",stdin);
    #endif
    //freopen("out.txt","w",stdout);
    int n;
Set();
while(cin>>n){
int cnt=0;
for(int i=5;i<=n;i++)
if(f[i]==2)cnt++;
cout<<cnt<<endl;
}
    return 0;
}