#include<cstdio>
#include<bitset>
using namespace std;
//ifstream f("ciur.in");
//ofstream g("ciur.out");
int nr,n,i,j;
bitset<2000000>p;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);

    p[1]=1;
    nr=0;
    for(i=2;i<=n;++i)
    {
        if(p[i]==0)
        {
            ++nr;
           // a[k]=i;
        }
    for(j=i+i;j<=n;j=i+j)
    {
        p[j]=1;
    }


}
printf("%d\n",nr);

    return 0;
}