#include <cstdio>
#include <bitset>
using namespace std;
bitset<2000000> p;
int n,i,j,nr;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    nr=0;
    for (i=1;i<=n;i++)p[i]=1;
    for (i=2;i<=n;i++)
    if (p[i]==1)
    {
        nr++;
        for (j=i*i;j<=n;j=j+i)p[j]=0;

    };
    printf("%d",nr);
    return 0;
}