#include<stdio.h>
#define INF 2000002
#include<bitset>

using namespace std;

int n,ans=0;
bitset<INF> sieve;

int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(long long i=2;i<=n;++i){
        if(i%10000==0)
            int a=1;
        if(sieve[i])continue;
        ans+=1;

        for(long long j=i*i;j<=n;j+=i)sieve[j]=1;
    }
    printf("%d",ans);
    return 0;
}