#include <cstdio>
using namespace std;
char prim[2000005];
void ciur (int n){
    int i,j,nr=0;
    for (i=2;i<=n;i++)
        prim[i]=1;
    for (i=2;i<=n;i++)
    {if (prim[i]==1){
        nr++;
    for (j=i+i;j<=n;j+=i)
    {prim[j]=0;}
    }
    }
        printf ("%d", nr);
}
int main(){
    freopen ("ciur.in", "r", stdin);
    freopen ("ciur.out", "w", stdout);
    int n;
    scanf("%d", &n);
    ciur(n);
    return 0;
}