#include<cstdio>
using namespace std;
int n,k;
char prim[2000004];
int main()
{
    freopen("ciur.in","r",stdin);
    scanf("%d",&n);
    for(int i=2; i<=n^(1/2); ++i)
    {
        if(!prim[i])
        {
            k++;
            for(int j=2; j*i<=n; ++j)
                prim[j*i]=1;
        }
    }
    freopen("ciur.out","w",stdout);
    printf("%d\n", k);
    return 0;
}