#include<stdio.h>
#define N 2000000
int main()
{
	freopen("ciur.in","r",stdin);
		freopen("ciur.out","w",stdout);
			char c[N+1];
				int cnt=0,n,i,j;
					scanf("%d",&n);
						//init
							for(i=2;i<=n;++i) c[i]=1;
								for(i=2;i<=n;++i)
									{
											if(c[i]) //daca i e prim
													{
																cnt++;
																			for(j=2*i;j<=n;j+=i) c[j]=0; //eliminam multiplii
																					}
																						}
																							printf("%d",cnt);
																								fclose(stdin);
																									fclose(stdout);
																										return 0;
																										}