#include <stdio.h>

bool a[2000005];
int n;

void torol(int x){
 int temp;
 temp=x+x;
 while(temp<=n){
  a[temp]=true;
  temp=temp+x;

 }

}

int main(){
int i,j,db=0;
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);

scanf("%d",&n);

for(i=2;i<=n;i++){
 if(!a[i]){
  ++db;
  torol(i);

 }
}

printf("%d",db);
return 0;}