#include <cstdio>


#define file_in "ciur.in"
#define file_out "ciur.out"

#define Nmax 2010100

int N,i,j,Nr,p[Nmax];

int main(){
	
	freopen(file_in,"r",stdin);
	freopen(file_out,"w",stdout);
	
	scanf("%d", &N);
	
	Nr=0;
	for (i=2;i<=N;++i)
		 if (p[i]==0){
			 Nr++;
			 for (j=i+i;j<=N;j+=i)
				  p[j]=1;
		 }
	
	printf("%d\n", Nr);

	return 0;
	
}