#include<cstdio>
using namespace std;
FILE *f,*g;
int x,i,j,p,nr;
bool a[3000000];
int main()
{f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
fscanf(f,"%d",&x);
for(i=3;i<=1415;i=i+2)
	if(a[i]==0)
		for(j=i*i;j<=2000000;j=j+i)
			a[j]=7;
j=1;
for(i=3;i<=x;i=i+2)
{if(a[i]==0)
{++j; }}
fprintf(g,"%d\n",j);
fclose(f);
fclose(g);
return 0;
}