#include<stdio.h>

using namespace std;

bool  a[2000003];
int i,j,k,n;

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