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

    g<<cnt<<"\n";
    return 0;
}