#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
int sum[1000005];
bool shai[1000005];
void dabiao(){
	for(int i=2;i<=1000000;i++){
		sum[i]=sum[i-1];
		if(!shai[i]){
			for(int j=2*i;j<=1000000;j+=i)
				shai[j]=1;
			sum[i]++;
		}
	}
}
int main()
{
	dabiao();
	int n;
	while(scanf("%d",&n)==1){
		printf("%d\n",sum[n]);
	}
}