#include<stdio.h>
FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
bool a[2000005];
int main()
{
	int n,i,j,nr;
	fscanf(f,"%d",&n);
	for(i=2;i<=n;i++)
		if(!a[i])
		{
			for(j=i*2;j<=n;j+=i)
				a[j]=1;
			nr++;
		}
	fprintf(g,"%d\n",nr);
	return 0;
}