#include<fstream.h>
int x[200001];
unsigned long int i,j,k,l,m,n;
int main(){
ifstream f("ciur.in");
ofstream g("ciur.out");
f>>n;
x[1]=1;
for(i=2;i<=2000000;i++)
	{if(i>2000000)break;
	if((x[i]==0)&&(i<=n))
		k++;
	if(x[i]==0)
	for(j=i*2;j<=2000000;j+=i)
		{if(j>2000000)
			break;
		x[j]=1;}
	}
g<<k;
f.close();
g.close();
return 0;
}