#include <iostream>
#include <vector>

int main(void)
{
  int n,r;
  while(cin >> n >> r){
    if(n == 0) break;
    vector<int> pill;
    int p,c;
    for(int i = n ; i >= 1 ; i--){
      pill.push_back(i);
    }
    for(int i = 0 ; i < r ; i ++){
      cin >> p >> c;
      vector<int> temp;
      for(int t = 0 ; t < p-1 ; t ++){
	temp.push_back(pill[t]);
      }
      for(int j = 0;
	  j < c;
	  j++)
	{
	  pill[j] = pill[j + p - 1];
	}
      copy(temp.begin(), temp.end(),
	   pill.begin() + c);
   }
    /*
    for(int i = 0; i < n; i++)
      {
	cout << pill [i] << " " ;
      }
    */
    cout << pill[0] << endl;
  }
}