#include <iostream>
#include <fstream>

std::ifstream f("ciur.in");
std::ofstream g("ciur.out");

const int NMAX = 2000000;
int n,sol;
bool v[NMAX + 5];

int main(){
    
    f >> n;
    
    sol = 1;
    
    v[0] = v[1] = true;
    for(int i = 4;i <= n;i += 2)
        v[i] = true;
    
    for(int i = 3;i <= n;i += 2)if(!v[i]){
        sol++;
        for(int j = i + i;j <= n;j += i)
            v[j] = true;
    }
    
    g << sol;
    
    return 0;
}