#include<cstdio>
using namespace std;
long n;
bool ciur[2000005];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&n);
    for (long i=1;i<=n;i++) ciur[i]=1;
    ciur[1]=0;
    for (long i=2;i<=n/2;i++) ciur[2*i]=0;
    for (long i=3;i<=n;i+=2)
        for (long j=2;j<=n/i;j++)
            {
                if (ciur[i]) ciur[i*j]=0;
            }
    long prime=0;
    for (long i=1;i<=n;i++) if (ciur[i]) prime++;
    printf("%ld",prime);
    return 0;
}