#include<stdio.h>
bool v[2000000];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int n,i,j,num=0;

    scanf("%d",&n);
     v[0]=1;
     v[1]=1;
    for(i=2;i<=n;i++)
     for(j=i*2;j<=n;j=j+i)
            v[j]=1;
    for(i=1;i<=n;i++)
        if(v[i]==0)
            {//printf("%d ",i);
             num++;
            }
       printf("\n%d",num);
    return 0;
}