#include <cstdio>

bool a[2000001];
int n,i,j,nrprime=0;

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