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

unsigned a[2000100];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    
    int n,ret=0,lim;
    
    scanf("%d",&n);
    if (n>=2) ++ret;
    lim = (int)sqrt(n);
    for (unsigned i=4;i<=n;i+=2) a[i>>16u]&= 1u<<(i&(1u<<16u));
    for (unsigned i=3;i<=n;i+=2) if(a[i>>31u]&(i&(1u<<31u)) == 0)
    {
        ++ret;
        if (i<=lim) for (unsigned j=i*i;j<=n;j+=2*i) a[j>>16u]&= 1u<<(j&(1u<<16u));
    }
    
    printf("%d\n",ret);
        
    return 0;    
}