#include <fstream>

using namespace std;

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

int C[2000005];

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

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

    int ct=0;

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

    outFile << ct;
}