#include <iostream>
#include <list>
#include <vector>
using namespace std;

int main(){
  int n, r;
  while(cin >> n >> r){
    vector<int> cards;
    if(n == 0 && r == 0){
      break;
    }
    int p, q;
    for(int i = 0; i < n; i++){
      cards.push_back(n - i);
    }
    for(int i = 0; i < r; i++){
      cin >> p >> q;
      p--;
      vector<int> temp, temp2;
      for(int i = 0 ;i < p; i++){
        temp.push_back(cards[i]);
      }
      for(int i = p; i < p + q; i++){
        temp2.push_back(cards[i]);
      }
      for(int i = 0; i < q; i++){
        cards[i] = temp2[i];
      }
      for(int i = 0; i < p; i++){
        cards[q + i] = temp[i];
      }
      
    }
    cout << cards[0] << endl;
  }
  return 0;
}