#include <fstream>
using namespace std;
int prime[1000000],ver[1000000]={0};
int main()
{
    ifstream f("ciur.in");
    ofstream c("ciur.out");
    int n,nr,i,j;
    f>>n;
    nr=0;
    ver[0]=ver[1]=1;
    for(i=4;i<=n;i=i+2)
        ver[i]=1;
    for(i=3;i<=n;i=i+2)
        if(ver[i]!=1)
            for(j=i*i;j<=n;j=j+2*i)
                ver[j]=1;
    prime[nr++]=2;
    for(i=3;i<=n;i=i+2)
        if(ver[i]!=1)
            prime[nr++]=i;
    c<<nr;
    return 0;
}