#include<stdio.h>
using namespace std;
bool v[2000001];
int main()
{
    int N,i,prim,j;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&N);
    prim=0;
    for(i=2;i<=N;i++)
    {
    if(v[i]==0)
    {
    prim++;
    for(j=2*i;j<=N;j+=i)
    v[j]=1;
    }
    }
    printf("%d\n",prim);
    return 0;
}