#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,val;
char c[2000001];
void ciur()
{
    int i,j;
    for(i=4;i<=n;i=i+2)
        c[i]=1;
    for(i=3;i<=n;i=i+2)
        if(c[i]==0)
        {
            val++;
            for(j=i*i;j<=n;j=j+i)
                c[j]=1;
        }
}

int main()
{
    fin>>n;
    if(n==2){
        fout<<1;
        return 0;
    }
    val++;
    ciur();
    fout<<val;
    return 0;
}