#include <iostream>
#include <cstdio>
using namespace std;

int p[2000000];

void prim(int a,int l)
{
    for(int d=a;d<=l;d=d+a)
        p[d]=1;
}

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