#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int n,cnt;
char prim[2000005];

int main(void)
{
    int i,j;
    in>>n;
    for(i=2;i<=n;i++)
        prim[i]=1;
    for(i=2;i<=n;i++)
        if(prim[i]){
            cnt++;
            for(j=i+i;j<=n;j+=i)
                prim[j]=0;
        }
    out<<cnt;
    return 0;
}