#include <fstream>
#include <iostream>
#include <cstdlib> //needed for exit function

using namespace std;

int fileSum(string filename);

int main() {
   string filename;
   cout << "Enter the name of the input file: ";
   cin >> filename;
   cout << endl;
   cout << "Sum: " << fileSum(filename) << endl;

   return 0;
}

int fileSum(string filename){
   ifstream obj;
   obj.open(filename);
   int sum = 0;
   if(!obj){
       cout<<"Error opening " << filename <<endl;
       exit(1);
   }
   else{
       int value;
       while(obj >>value){
           sum = sum + value;
       }
   }
   return sum;
}