#include <stdio.h>
#include <math.h>

//0 0 0 1 0 1 0 1 1
//1 2 3 4 5 6 7 8 9 

char v[2000001];

int n,s,ri,i,j;
char p;

int main(){
	FILE *f = fopen("ciur.in","r");
	fscanf(f,"%d",&n);
	fclose(f);
	
	s = 0;
	for (i=2;i<=n;i++) {
		if (v[i]==0) {
			s++;
			for (j=i+i;j<=n;j+=i)
				v[j] = 1;
		}
	}
	
	FILE *g = fopen("ciur.out","w");
	fprintf(g,"%d",s);
	fclose(g);
	
	return 0;
}