#include <stdio.h>
#include <math.h>

char a[2000100];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    
    int n,ret=0;
    
    scanf("%d",&n);
    if (n>=2) ++ret;
    
    for (int i=4;i<=n;i+=2) a[i] = 1;
    
    for (int i=3;i<=n;++i) if(a[i] == 0)
    {
        ++ret;
        for (int j=i*i;j<=n;j+=2*i) a[j] = 1;        
    }
    
    printf("%d\n",ret);
        
    return 0;    
}