#include <cstdio>
bool ciur[2000023];
int n;
int main()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
    {
        if(i*i<0) break;
        if(ciur[i]==1) continue;
        for(int j=i*i;j<=n;j+=i) ciur[j]=1;
    }
    int ct=0;
    for(int i=2;i<=n;i++) if(!ciur[i]) ++ct;
    printf("%d\n",ct);
}