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

double long v[2000001];
int main(){
    double long i,j,n,d=0;
	
    
	ifstream f("ciur.in");
    ofstream g("ciur.out");
	
    f>>n;
    for(i=2;i<=n;i++)if(!v[i]){
								d++;
								for(j=i+i;j<=n;j=j+i)
								v[j]=1;
}
	
    g<<d;
	
    return 0;

}