#include <fstream>

using namespace std;

ifstream inFile("ciur.in");
ofstream outFile("ciur.out");

bool C[2000005];

int main()
{
    int n;
    inFile >> n;

    for(int i = 2; i <= n/2; i++ ){
        if( C[i] == 0 ){
            int j = i + i;
            while(j <= n){
                    C[j] = 1;
                    j+=i;
            }
        }
    }

    int ct=0;

    for(int i = 2; i <= n; i++)
        if( C[i] == 0 ) ct++;

    outFile << ct;
}