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