#include <bits/stdc++.h>
using namespace std;
ifstream f("prim.in");
ofstream g("prim.out");
bitset <2000002>a;
int prime[150001];
int i,j,nr=1,k,N;
void Ciur()
{
    prime[1]=2;
    for(i=3;i*i<=N;i++)
    if(a[i]==0)
    for(j=i*i;j<=N;j+=i)a[j]=1;

    for(i=3;i<=N;i+=2)
    if(a[i]==0)prime[++nr]=i;

    //for(i=1;i<=nr;i++)g<<prime[i]<<"\n";
}
int main()
{
    f>>N;
    Ciur();
    ///cout<<(al k+1-lea numar prim)^2;
    g<<nr;
    //g<<(long long)(prime[k+1])*prime[k+1];
    return 0;
}