D_i_v_i_z_o_r_i_3

#include <iostream>
#include <cmath>
#define NN 100000
using namespace std;
int a,b,A,B,c,v[NN];

int main()
{
	v[0]=v[1]=1;
	for(int i=2;i*i<NN; ++i)
		if(v[i]==0)
			for(int j=2;i*j<NN;++j)
				v[i*j]=1;
	cin>>a>>b;
    while(sqrt(a)!=(int)sqrt(a))
        ++a;
    while(sqrt(b)!=(int)sqrt(b))
        --b;
	for(int i=(int)sqrt(a);i<=(int)sqrt(b);++i)
		if(v[i]==0)
			++c;
	cout<<c;
	return 0;
}