#include <iostream>
#include <cstdio>
#include <cstring>
#define Nmax 2000005
using namespace std;

int N,Nr;
int P[Nmax];

void Rezolvare()
{
    memset(P,1,sizeof(P));
    for(int i=2;i<=N;++i)
        if(P[i])
        {
            Nr++;
            for(int j=i+i;j<=N;j+=i)
                P[j]=0;
        }
}

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&N);
    Rezolvare();
    printf("%d",Nr);
    return 0;
}