#include<stdio.h>
#include<stdlib.h>
#include<math.h>
using namespace std;
int n,i,d,flag,q=2,I;
int main()
{
    FILE * f;  f=fopen("ciur.in","r"); FILE * g; g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    for(i=3;i<=n;i+=2)
    {
        I=sqrt(i);
        for(d=3;d<=I;d+=3)
            if(i%d==0) flag=0;
            else flag =1;
        if(flag==1) q++;
    }
    fprintf(g,"%d",q);
    fclose(f); fclose(g);
    return 0;
}