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

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

int main()
{
    int prim[2005],cnt=0,N;
    f>>N;
    for(int i=2;i<=N;i=i+1){
        prim[i]=1;
    }
    for(int i=2;i<=N;i=i+1){
        if(prim[i]){
            cnt++;
            for(int j=i+i;j<=N;j=j+i){
                prim[j]=0;
            }
        }
    }
    g<<cnt;
    return 0;
}