#include<fstream>
#define N 2000002
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool prim[N];
int n,s;
int ciur(){
    int i,j;
    for (i=2;i<=n;i++) prim[i]=1;
    for(i=2;i<=n;i++)
        if(prim[i]){
            s++;
        for (j=i+i;j<=n;j+=i) prim[j]=0;
    }
    return s;
}
int main(){
    in>>n;
    out<<ciur();
    return 0;
}