#include<stdio.h>

long int n,p[2000001],np;
long int i,j;
int main()
{

FILE *in=fopen("ciur.in","r");
FILE *out=fopen("ciur.out","w");
fscanf(in,"%ld",&n);
np=1;
for(i=3;i<=n;i=i+2)
{
 if(p[i]==0)
 {
	np++;
	for(j=i*i;j<=n;j=j+i)
	p[j]=1;
 }
}
fprintf(out,"%ld",np);
return 0;
}