// 2004‘“ΰ—\‘IA Hanafuda Shuffle

#include <iostream>
#include <algorithm>

using namespace std;

int main(){
	int n, r;
	int card[50];
	while(cin >> n >> r, n){
		for(int i=0;i<n;i++) card[i] = n-i;
		for(int i=0;i<r;i++){
			int p, c; cin >> p >> c;
			rotate(card, card+p-1, card+p+c-1);
		}
		cout << card[0] << endl;
	}
}