#include <fstream>

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