#include <cstdio>

using namespace std;

bool a[2000010];

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