#include<cstdio>
#include<bitset>
using namespace std;
int t,n;
bitset <2000001>s;
void ciur()
{
    int i,j;
    for (i=2;i<=n;++i)
    {
        if (s[i]==0)
        {
            ++t;
            for (j=2;i*j<=n;++j) s[i*j]=1;
        }
    }
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    ciur();
    printf("%d",t);
return 0;
}