#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int v[2000001];
int main()
{
    int n,i,j,nrp;
    in>>n;
    nrp=n-1;
    v[0]=1;
    v[1]=1;
    for(i=2; i*i<=n; i++)
        if(v[i]==0)
            for(j=i*i; j<=n; j=j+i )
                {v[j]++;
                 if(v[j]==1)
                 nrp--;
                }
    out<<nrp;
    return 0;
}