#include "stdio.h"
#include "math.h"

#define fr(i,a,b) for(int i=a;i<b;++i)
#define N 2000010

bool t[N]={0};

int main()
{
    long n;
    int h=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&n);
    fr(i,2,sqrt(n))
    {
        if(!t[i])
            for(int j=i*i;j<n;j+=i)
                t[j]=true;
    }
    fr(i,2,n)
        if(!t[i]) ++h;
    printf("%d",h);
    return 0;
}