#include <fstream>
using namespace std;

int N,contor=1;
char prim[2000000];

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int main() {
    int i,j;
    cin>>N;
    for( i =1; (i << 1) + 1 <= N;i+=1){
        if(prim[i] == 0){
            contor++;
        for(j=3*i+1; (j << 1) + 1 <= N;j += (i << 1) + 1){
            prim[j] =1;
        }
    }
    }
    cout<<contor;
}