#include <cstdio>
#define N 2000001
using namespace std;
bool p[N];

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