#include<stdio.h>
#define INF 2000001

using namespace std;

int n,ans=0;
bool sieve[INF];

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