#include <iostream>
#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000014];

int main()
{
    int n,s=1,i,j;
    cin>>n;
    v[0]=1;
    v[1]=1;
    for(i=4;i<=n;i=+2)
        v[i]=1;
    for(i=3;i<=n;i+=2)
        if(!v[i]){
            for(j=2*i;j<=n;j=j+i)
                v[j]=1;
            s++;
        }
    cout<<s;
    return 0;
}