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

ifstream fin("ciur.in");
ofstream fout("ciur.out");

char prim[2000005],n,cnt;

int main()
{
    int n,cnt=0;
    fin>>n;
    for(int i=2;i<=n;i++)
        prim[i]=1;
    for(int i=3;i<=n;i+=2)
        if(prim[i])
        {
            cnt++;
            for(int j=i+i;j<=n;j+=i)
              prim[j]=0;
        }
    fout<<cnt+1;
}