import std.stdio;
import std.algorithm;
import std.string;
import std.range;
import std.array;
import std.conv;
import std.complex;
import std.math;
import std.ascii;
import std.bigint;
import std.container;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

const real eps = 1e-10;

void main(){
	while(true) {
		auto nr = readInts();
		auto n = nr[0];
		auto r = nr[1];
		if(n == 0 && r == 0) {
			return;
		}
		int[] cards = array(iota(n));
		reverse(cards);
		for(int i = 0; i < r; ++i) {
			auto pc = readInts();
			auto p = pc[0];
			auto c = pc[1];
			cards = cards[p-1..p-1+c] ~ cards[0..p-1] ~ cards[p-1+c..$];
		}
		writeln(cards[0]+1);
	}
}