#include <fstream>

using namespace std;
char v[2000005];
int main()
{
    int i,j,n,cnt;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    cnt=0;
    for(i=4;i<=2000000;i+=2) v[i]=1;
    for(i=3;i*i<=2000000;i+=2)
    {
        if(v[i]==0) for(j=i*i;j<=2000000;j+=i) v[j]=1;
    }
    for(i=2;i<=n;i++)if(v[i]==0)cnt++;
    g<<cnt;
    return 0;
}