#include<iostream>
using namespace std;
int br=0, c, x=1, k, a, b;
int prime (int c)
{
    x++;
    if (x==c/2+1) {x=1;return 0; }
    else if(c%x==0) {x=1;return 1; }
    else return prime(c);
}

int main(){
cin>>k;
cin>>a>>b;
for(int j=0; j<k; j++)
{
    cin>>a>>b;
    for(int i=a; i<=b; i++)
    {
        if(i==2 || i==3) br++; //cout<<"2 or 3 "<<endl;}
        else if(prime(i)==1) 
        {
            br++;
            //cout<<i<<" "<<prime(i)<<endl;
        }
    }
}

//if(prime(i)==0) br++;
cout<<br<<endl;
return 0;
}