#include <cstdio>
#include <cmath>
#define MAX 2000005

using namespace std;

int n,k;
bool v[MAX];

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])
            for(int j=i*i;j<=n;j+=i)
                v[j]=1;
    k=0;
    for(int i=2;i<=n;i++)
        (!v[i])? k++:0 ;
    printf("%d",k);
    return 0;
}