#include <stdio.h>
long n;
int prim[2000001];
FILE *f,*g;
int main(){
	long i,j,nr=0;
	f=fopen("ciur.in","r");
	fscanf(f,"%ld",&n);
	fclose(f);
	for (i=2;i<=n;i++)
		prim[i]=1;
	for (i=2;i<=n;i++)
		if (prim[i])
		{
			nr++;
			for (j=i+i;j<=n;j+=i)
				if (prim[j])
					prim[j]=0;
		}
	g=fopen("ciur.out","w");
	fprintf(g,"%ld\n",nr);
	fclose(g);
	return 0;
}