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

int main()
{
    ifstream in;
    in.open("ciur.in");
    ofstream out;
    out.open("ciur.out");
    int nr,i,j,sum = 0;
    in >> nr;
    int *arr = new int[nr];
    arr[0] = 1;
    arr[1] = 1;
    if(nr >= 2)sum++;
    for(i = 4; i <=nr; i+=2){
        arr[i] = 1;
    }
    for(i = 3; i <=nr; i+=2){
        if(arr[i] == 0){
            sum++;
            for( j = 2; j * i <= nr; j++){
                arr[j*i]=1;
            }
        }
    }
    out<< sum<<endl;
    return 0;
}