#include <iostream>
#include <vector>
#include <algorithm>
#include <string.h>
using namespace std;

const int MAX_N = 1000000;

vector<int> init(void){
    vector<int> prime;
    bool is_prime[MAX_N];
    memset(is_prime, true, MAX_N);
    
    is_prime[0] = is_prime[1] = false;
    for(int i=2; i<MAX_N; i++){
        if(is_prime[i]){
            prime.push_back(i);
            for(int j=2*i; j<MAX_N; j+=i) is_prime[j] = false;
        }
    }
    return prime;
}

int main(int argc, const char * argv[])
{
    int n;
    vector<int> prime = init();
    while(cin>>n){
        cout << upper_bound(prime.begin(), prime.end(), n)-prime.begin() << endl;
    }
    return 0;
}