#include<cstdio>
#include<stdlib.h>

using namespace std;

int main()
{
int n,i,j,ct;
unsigned char prim[2000005];
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    
    scanf("%d",&n);
    ct=0;
    for (i=2;i<=n;i++)
        prim[i]=1;
    for (i=2;i<=n;i++)
        if (prim[i])
        {
             ++ct;
             for (j=i+i;j<=n;j+=i)
             prim[j]=0;
             }
    printf("%d",ct);

return 0;
}