#include <iostream>
#include <fstream>
#define NMax  2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int N,prim[NMax],c,i,j;
int main()
{
fin>>N;
for(i=2;i<=N;i++)
    prim[i]=1;
for(i=2;i<=N;i++)
{
    if(prim[i]==1)
    {
        c++;
        for(j=i+i;j<=N;j+=i)
            prim[j]=0;
    }
}
fout<<c;
    return 0;
}