#include <cstdio>
using namespace std;
int n,k=1;
bool neprim[2000001];
void ciur()
{
    for(int i=3;i*i<=n;i+=2)
        if(!neprim[i])
            for(int j=i+i;j<=n;j+=i)
                neprim[j]=1;

    for(int i=3;i<=n;i+=2)
        if(!neprim[i])
            ++k;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    ciur();
    printf("%d",k);
    return 0;
}