def check_SNT(n):
    flag = True
    if (n < 2):
        flag = False
    elif (n == 2):
        flag = True
    elif (n % 2 == 0):
        flag = False
    else:
        for i in range(3, n, 2):
            if (n % i == 0):
                flag = False
 
    return flag
d=0
a=int(input())
b=int(input())
for i in range(a,b+1):
    if (check_SNT(i)):
        d=d+1 
print(d)

uses crt;

var a,b,i: word;

function nt(n: word): boolean;

var i,d: word;

begin

d:=0;

for i:=1 to n do

if n mod i=0 then inc(d);

if d=2 then nt:=true elsent:=false;

end;

begin

clrscr;

write ('nhap a,b: ');   readln (a,b);

writeln ('trong doan [',a,'..',b,'] co cac so nguyen to la: ');

for i:=a to b do

if nt(i) then Write (i:4);

readln;

end.