#include<stdio.h>

FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

char v[2000001];
int i,j,nrp,n;

int main() {

	fscanf(f,"%d",&n);
	for (i=2;i<=n;i++) {
		if (v[i] == 0) {
			nrp++;
			for (j=2*i;j<=n;j+=i)
				v[j] = 1;
		}
	}
	fprintf(g,"%d",nrp);

	fclose(f);
	fclose(g);
	return 0;
}