这个计算素数的程序能走多远

#include <iostream>
using namespace std;
int ifprime(long long int);
int main()
{
    long long int number;   
    cout<<"Enter the number of prime numbers you want to know:n";
    cin>>number;    //number is the number of prime numbers to be displayed
    long long int j=0;
    long long int m=2;      //m would be used as consecutive natural numbers on which, test of prime number is performed
    while (1<2)
    {
        if(ifprime(m)==1)
        {
            j+=1;   // j is the counter of the prime numbers found and displayed
            cout<<m<<endl;
        }
        m+=1;
        if(j==number)
        {
            break;
        }
    }
}
int ifprime(long long int a)
{
    for(int i=2;i<a;i++)
    {
        if(a%i==0)
        {
            return 0;
        }
    }
    return 1;
}

与已知最大的素数相比，long long int的范围似乎很小：/

即使我要计算long long int范围内的最后一个素数，我能计算出计算该数所需的时间吗？