#include <iostream>
#include <fstream>

#define NN 2000005

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

long long n, v[NN];

int main(){
    v[0] = v[1] = 1;
    for(int i=2;i*i<NN; ++i)
        if(v[i]==0)
            for(int j=2;i*j<NN;++j)
                v[i*j] = 1;
    fin >> n;
    int x,C = 0;
    for(int i=1;i<=n;++i){
        if(v[i]==0)
            C ++;
    }
    fout << C;
    return 0;
}