# include <bitset>
# include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int p,n,i,j;
bitset <1000000>v;
int main(){
    f>>n;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            for(j=i*i;j<=n;j=j+i)
                v[j]=1;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            p++;
    g<<p<<'\n';
    g.close();
    return 0;
}