#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <string>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
using namespace std;

int main()
{
  int n, r;
  while(cin >> n >> r, n || r){
    vector<int> pile(n);
    for(int i = 0; i < pile.size(); ++i)
      pile[i] = i + 1;
    
    for(int i = 0; i < r; ++i){
      int p, c;
      cin >> p >> c;
      // n-p-c+1 から c 枚を上に持っていく
      vector<int> newpile(n);
      int j = 0, k = 0;
      while(j < n - p - c+1)
	newpile[k++] = pile[j++];
      j += c;
      while(j < n)
	newpile[k++] = pile[j++];
      j = n - p - c+1;
      while(k < n)
	newpile[k++] = pile[j++];
      pile = newpile;
    }
    cout << pile.back() << endl;
  }
}