#include <iostream>
#include <bitset>
using namespace std;

bitset<2000001> p;

int main(){
    p[0]=1;
    for(int i = 3; i <= 2000000; i+=2)
        if(p[i/2]==0)
            for(int j = 3 * i; j <= 2000000; j += 2 * i)
                p[j/2] = 1;
    int n, k = 1;
    cin >> n;
    for(int i = 1; i <= n; i += 2){
        if(p[i / 2] == 0){
            k++;
        }
    }
    cout << k;
    return 0;
}