#include<fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int n,cnt,i,j,x[2000000];

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