#include <iostream>

using namespace std;

int main()
{
  int n, r;
  while(cin >> n >> r) {
    if(n == 0 && r == 0)
      break;

    int array[n + 1];

    for(int i = 0; i < n; i++)
      array[i + 1] = n - i;

    while(r--) {

      int a, b;
      cin >> a >> b;

      int tmp[n + 1];

      for(int i = a ; i<= b + a; i++)
        tmp[i] = array[i];
    
      for(int i = a - 1; i >= 1; i--)
        array[i + b] = array[i];
    
      for(int i = 1; i <= b; i++)
        array[i] = tmp[i + a - 1];

    }

    cout << array[1] << endl;
  }
  return 0;
}