#include <cstdio>

using namespace std;

int n;
char c[2000005];

int ciur(int n)
{
    int nr=0;
    for(int i=2;i<=n;i++)
    {
        if(c[i]==0)
        {
            nr++;
            for(int j=i*2;j<=n;j+=i)
                c[j]=1;
        }
    }
    return nr;
}

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    scanf("%d",&n);

    printf("%d",ciur(n));

    return 0;
}