お金が引き出せない銀行 [MISSION LEVEL: D]

#include <bits/stdc++.h>
#define _for(i,a,b) for(int i = (a);i < (b);i ++)
#define pb push_back
using namespace std;

int main()
{
    int a,b;
    while(cin >> a >> b)
    {
        if(a>b)
            cout << a-b << endl;
        else
            cout << "error" << endl;
    } 
    return 0;
}