#include <cstdio>

using namespace std;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    bool prim[2000005];
    int i,j,n,nrprim=0;

    scanf("%d",&n);
    for(i=2;i<=n;i++)
        prim[i]=1;
    for(i=2;i<=n;i++)
        if(prim[i]==1)
        {
            nrprim++;
            for(j=i+i;j<=n;j+=i)
                prim[j]=0;
        }
    printf("%d",nrprim);
    return 0;
}