#include <iostream>
#include <fstream>

using namespace std;
int a[2000000]={1};
int main()
{
    freopen("f.in","r",stdin);
    freopen("f.out","w",stdout);
    int n,nr=1,c=1;
    scanf("%d",&n);
    if(n==2)
      printf("1");
    else
     {
        for(int i=3;i*i<=n;i+=2)
           if(a[i]==0)
            for(int j=i*i;j<=n;j+=i)
              a[j]=1;
     }
     for(int i=3;i<=2000000;i+=2)
        if(a[i]==0)
          nr++;

      printf("%d",nr);
    return 0;
}