#include <iostream>
#include <math.h>
#include <fstream>

using namespace std;
int n,cnt;
bool p[2000005];

int main()
{
    int i,j;
    ifstream fin("ciur.in");
    fin>>n;
    fin.close();
    for(i=2;i<=n;i++)
    {
        if(p[i]==0)
        {
            cnt++;
            for(j=i+i;j<=n;j+=i)
                p[j]=1;
        }
    }
    ofstream fout("ciur.out");
    fout<<cnt;
    fout.close();
    return 0;
}