#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool v[2000005];

int main()
{
    int n,rasp=0;
    fin>>n;
    for(int i=2;i*i<=n;i++){
        if(v[i]==true){
            continue;
        }
        for(int m=2*i;m<=n;m+=i){
            v[m]=1;
        }
    }
    for(int j=2;j<=n;j++)
    {
        if(v[j]!=1)
            rasp++;
    }
    fout<<rasp;

    return 0;
}