#include <iostream>
#include <fstream>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,k,j;
bool c[2000005];
int main()
{
    f>>n;
    for(i=2;i<=n;i++){
        if(c[i]==0)k++;
        if(i==2||i%2!=0){
            for(j=i;j<=n;j=j+i)
                c[j]=1;
        }
    }
    g<<k;
    return 0;
}