#include<fstream>
#define nmax 2000005
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out"); 
int n,count;
char used[nmax];  
int main()
{
    int i,j;
    f>>n;
    for(i=2; i<=n; ++i)
        used[i]=1;
    for(i=2; i<=n; ++i)
        if(used[i])
        {
            ++count;
            for(j=i+i; j<=n; j+=i)
                used[j]=0;
        }
    g<<count<<"\n";
    return 0;
}