#include <cstdio>
const   int max = 2000005;
using namespace std;
int n;
char a[max];
int main(){
    int i, j, p = 0;
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf("%d",&n);
    for (i=2;i<=n;++i) a[i] = 1;

    for (i=2;i<=n;++i)
        if (a[i]==1) {
            ++p;
            //printf("%d ",i);
            for(j=i+i;j<=n;j+=i) a[j] = 0;
        }
    printf("%d\n",p);
    return 0;
}