#include <cstdio>
#include <bitset>

using namespace std;
int i,aux,n,b,k,j,p,m,s;
long long cont;
#define dim 2000001
//char v[dim];

bitset <dim> ciur;

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

    scanf("%d",&n);
    for(i=1;i<=n;i++) ciur[i]=1;
    ciur[1]=0;
    for(i=2;i<=n;++i)
        if (ciur[i]==1){
            cont++;
            for(j=2;j<=n/i;++j)
                ciur[i*j]=0;

        }


    printf("%d\n",cont);

}