#include <iostream>
#include <stl.h>

using namespace std;

int main()
{
    int n,r,c,p;
    while(cin >> n >> r , n && r)
    {
	vector<int> st;
	for(int i = 1 ; i <= n ; i++)st.push_back(i);
	while(r--)
	{
	    cin >> p >> c;
	    reverse(st.begin()+n-p+1,st.end());
	    reverse(st.begin()+n-p+1-c,st.end());
	    reverse(st.begin()+n-c,st.end());
	}
	cout << st.back() << endl;
    }
    return 0;
}