#include <fstream>
#include <math.h>

using namespace std;

int v[2000010];

int main(){
    for(int i=2;i<sqrt(2000000);i++)
        if(v[i]==0)
        for(int j=i+i;j<=2000000;j=j+i)
        v[j]=1;
    ifstream in ("ciur.in");
    ofstream out ("ciur.out");
    int n,S;
    S=0;
    in>>n;
    for(int i=2;i<=n;i++){
        if(v[i]==0)
            S++;
    }
    out<<S;
    in.close();
    out.close();
    return 0;
}