#include<cstdio>
using namespace std;
int v[2000001];
int prim(int X)
{
int i;
for (i = 2; i * i <= X; ++i)
	if (X % i == 0)
		return 0;
return 1;

}
int main(){
	int n,nr=0,j,i;
	FILE * pFile;
	pFile=fopen("ciur.in","r");
	fscanf(pFile,"%d",&n);
	for(i=2;i<=n;i++){
		if(v[i]==0){
			if(prim(i))
				for(j=i;j<=n;j++)
					if(j%i==0)
						v[j]=-1;
		v[i]=1;}
		if(v[i]==1)nr++;
	}
	pFile=fopen("ciur.out","w");
	fprintf(pFile,"%d",nr);
	return 0;
}