#include <iostream>
#include<fstream>
#include<bitset>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,k,sol;
bitset<2000010> p;
int main()
{
    f>>n;
    sol=1;
    for(i=3;i*i<=n;i+=2)
    {
        if(!p[i])
        {
            sol++;k=2*i;
            for(j=i*i;j<=n;j+=k)
            p[j]=1;
        }
    }
    for(;i<=n;i+=2)
        if(!p[i])
        sol++;
    g<<sol;
    return 0;
}