#include<stdio.h>
#include<math.h>
FILE *f1,*f2;
long a,b,i,j,n;
char v[2000003];
int main(){
	f1=fopen("ciur.in","r");
	f2=fopen("ciur.out","w");
	fscanf(f1,"%ld",&n);
	for(i=1;i<=n;v[i]=0,i++);
	a=floor(sqrt(n))+1;
	i=2;
	b=0;
	while(i<=n){
		if(!v[i]){
			b++;
			if(i<a){
				for(j=i*2;j<=n;v[j]=1,j=j+i);
			}
		}
		i++;
	}
	fprintf(f2,"%ld",b);
	return 0;
}