#include <iostream>
#include <fstream>
#define Nmax 2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool ok[Nmax];
int main()
{
    int i,j,n,cnt=0;;
    fin>>n;
    ok[1]=1;
    for(i=2;i<=n;++i)
    {
        if(!ok[i])
        {   ++cnt;
            for(j=i+i;j<=n;j+=i)
                ok[j]=1;
        }
    }
    fout<<cnt;
    return 0;
}