#include<fstream>
using namespace std;
int n, i, j, nr;
char v[2000001];
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main(){
    fin>> n;
    v[0] = 1;
    v[1] = 1;
    for(i = 2; i <= n; i++){
        if(v[i] == 0){
            for(j = i + i; j <= n; j+= i){
                v[j] = 1;
            }
        }
    }
    for(i = 1; i <= n; i++){
        if(v[i] == 0){
            nr++;
        }
    }
    fout<< nr;
    return 0;
}