#include <cstdio>
#define Nmax 2000005

using namespace std;

char e[Nmax];
int n,nr;

FILE *fin=freopen("ciur.in","r",stdin);
FILE *fout=freopen("ciur.out","w",stdout);

void eratostene()
{
    e[1]=1;
    for(int i=2;i<=n;i++)
        e[i]=1;
    for(int i=2;i<=n;i++){
        if(e[i])
        {
            nr++;
           for(int j=i+i;j<=n;j+=i)
            e[j]=0;
        }
    }
    printf("%d\n",nr);
}

int main()
{
    scanf("%d", &n);
    eratostene();
    return 0;
}