#include<stdio.h>
#include<bitset>
#include<algorithm>
#include<math.h>

using namespace std;

#define nmax 2000010

int n,t;
bitset<nmax> v;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(int i=2;i<=sqrt(n);++i)
    {
        if(v[i]==0)
    {
        for(int j=i*i;j<=n;j+=i)
            v[j]=1;
    }
    }
    for(int i=2;i<=n;++i) if(v[i]==0) t++;
    printf("%d",t);
}