#include <cstdio>
#define nmax 2000010

using namespace std;

int p[nmax];

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

    int n,i,j,nr=0;
    scanf("%d",&n);
    for(i=2;i<=n;i++)
        {
            if(!p[i])
               nr++;
            for(j=2*i;j<=n;j+=i)
                p[j]=1;
        }
    printf("%d",nr);

    return 0;
}