#include<stdio.h>
#include<math.h>
int isprime(int x){
	int i=3;
	while( i <= sqrt(x) ){
		if(x%i==0)return 0;
		i = i + 2;
	}
	return 1;
}
int main(){
	int n,c;
	while(scanf("%d",&n)!=EOF){
		c=1;
		for(int i=3;i<=n;i+=2)if(isprime(i))c++;
		printf("%d\n",c);
	}
	return 0;
}