#include<fstream>
#include<vector>
#define NMAX 2000005

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

//data
std::vector<bool>primes(NMAX);
int n, count = 0;


//read data
void readData(){
    f >> n;
}


//solve 
void ciur(){
    count = 1;
    for(int i = 3; i<=n; i+= 2){
        if(!primes[i]){
            count ++;
            for(int j = i; j<=n; j+=2*i){
                primes[j] = true;
            }
        }
    }
}

int main(){
    readData();
    ciur();
    g << count << '\n';
    return 0;
}