#include <cstdio>


using namespace std;

int ciur[2000000];


int main()
{


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

    printf("%d\n",p);

    return 0;
}