#include <cstdio>
#define nmax 2000005

using namespace std;

int n;
bool a[nmax];

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