#include<iostream>

#define rep(i,n) for(int i=0; i<n; i++)

int main(){
	int yama[51];
	int n,r;
	int tmp[51];

	while(std::cin >> n >> r && (n || r)){
		int c,p;
		rep(i,n){
			yama[i] = n-i;
		}
		rep(i,r){
			std::cin >> p >> c;
			rep(j,c){
				tmp[j] = yama[p-1+j];
			}
			rep(k,p-1){
				yama[p-1+c-k-1] = yama[p-1-k-1];
			}
			rep(l,c){
				yama[l] = tmp[l];
			}
		}
		std::cout << yama[0] << std::endl;
	}

	return 0;
}