#include<stdio.h>
#include<malloc.h>

int main()
{
	FILE* f1,*f2;
	f1=fopen("ciur.in","r");
	f2=fopen("ciur.out","w");
	int N,count=0,i;
	fscanf(f1,"%d",&N);
	int *a=(int*)malloc(N*sizeof(int));
	for(i=2;i<=N;i++)
	{
		if(a[i]!=-1)
		{
		  count++;
		  for(int j=i*i;j<=N;j+=i)
			 a[j]=-1;
		}
	}
	fprintf(f2,"%d\n",count);
	free(a);
    return 0;
}