#include <iostream>
#include <fstream>

using namespace std;

int n,m;
char prim[2000005];

void fct()
{
    for(int i=2;i<=n;++i)
        prim[i]=1;
    for(int i=2;i<=n;++i)
        if(prim[i])
        {
            m++;
            for(int j=i+i;j<=n;j+=i)
                prim[j]=0;
        }
}

int main()
{
    ifstream fin("ciur.in");
    fin>>n;
    fct();
    ofstream fout("ciur.out");
    fout<<m;
    return 0;
}