#include <stdio.h>
using namespace std;

int n, nr=1;
bool prim[2000001];

int main()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);

    scanf("%d", &n);

    for(int i=3;i<=n;i+=2)
        if(!prim[i])
        {
            nr++;
            for(int j=i+i;j<=n;j+=i)
                prim[j]=true;
        }
    printf("%d", nr);
    return 0;
}