#include<stdio.h>
unsigned long n,j,i,q=1; bool a[1999999];
int main(){
	FILE*f=fopen("ciur.in", "r");
	fscanf(f,"%lu",&n);
	fclose(f);
	FILE*g=fopen("ciur.out","w");
	if(n%2==0) n--;
	for(i=3;i<=n;i+=2)
		if(a[i]==0){
			for(j=3;j*i<=n;j+=2) a[j*i]=1;
			q++;
		}
	fprintf(g,"%lu",q);

	fclose(g);
	return 0;
}