#include <bits/stdc++.h>
using namespace std;

int C(int n,int r){
    if(r==0){
        return -1;
    }else return C(n,r-1)*(n-r+1)/r;
}

int main(){
    int n,r;
    while(cin>>n>>r){
        if(n==0&&r==0)break;
        if(C(n,r)==0)cout<<"error!"<<endl;
        else cout<<-C(n,r)<<endl;
    }
}