#include <cstdio>
#include <cmath>
using namespace std;
const int NMAX=2000000;
bool c[NMAX+5];
void ciur(int n)
{
    int lim,i,j;
    c[1]=c[2]=1;
    lim=(int)sqrt((double)n);
    for(i=4;i<=n;i+=2)
        c[i]=1;
    for(i=3;i<=lim;i+=2)
    if(c[i]==0)
        for(j=i*i;j<=n;j+=2*i)
        c[j]=1;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n;
    scanf("%d",&n);
    int k=1,i;
    ciur(n);
    for(i=3;i<=n;i+=2)
    if(c[i]==0)
    ++k;
    printf("%d",k);
    return 0;
}