#include <fstream.h>
void main() {

ifstream f("ciur.in");
ofstream g("ciur.out");
int arr[99999]= {2};
int n,temp,nr=0;
f>>n;

for(int i = 3;i<=n;i +=2){
arr[i] = 1;
}

for(int i = 3; i<=n;i +=2) {
if(arr[i] == 1) {
for(temp=2;temp*i<=n;temp++) {
arr[i*temp] = 0;
}
}
}
for(int i = 3; i<=n;i +=2) {
if(arr[i] == 1) {
nr++;
}
}
g<<nr;
f.close();
g.close();
}