#include <cstdio>
using namespace std;

int n;
int marcare[2000000];
int nr;


void rezolvare(){
    for(int i=2;i<=n;++i)
        if(marcare[i]==0){
            nr++;
            for(int j=i+i;j<=n;j+=i)
                marcare[j]=1;
        }
    printf("%d",nr);
}

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    rezolvare();
    return 0;
}