#include <cstdio>

using namespace std;

int n,nr;
char prim[2000005];

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