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