#include<fstream>
#include<cmath>0
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char n,i,sol,v[2000001],j;
int main(){ 
	fin>>n;
	for(i=1;i<=n;i++)
		fin>>v[i];
	for(i=2;i<=n;i++)
		if(v[i]==0){
			sol++;
			for(j=i+i;j<=n;j+=i)
				v[j]=1;
		}
	fout<<sol;
	return 0;
}