//#define NDEBUG

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>

#include <list>
#include <set>
#include <map>
#include <vector>

using namespace std;

#undef max
#undef min
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))

#ifdef NDEBUG
#define dprintf
#else
#define dprintf printf
#endif

int chomp(char *s)
{
	int len;
	
	len = strlen(s);
	while(len > 0 && (s[len-1] == '\r' || s[len-1] == '\n'))
		s[--len] = '\0';

	return len;
}


int main()
{
	int cards[50];
	int taihi[50];
	int i, j;
	int n, r;
	int k, l;
	int p, c;
	int temp;

	while(1) {
	
	scanf("%d", &n);
	scanf("%d", &r);
	if(n==0 && r==0)
		break;

	for(i=0; i<=n; i++)
		cards[i] = n - i;
		
	for(l=0; l<r; l++) {
		scanf("%d %d", &p, &c);
		for(j=0; j<c; j++)
			taihi[j] = cards[p+j-1];
		for(j=p-2; j>=0; j--)
			cards[j+c] = cards[j];
		for(j=0; j<c; j++)
			cards[j] = taihi[j];
	}
	
	printf("%d\n", cards[0]);	
	}
	return 0;
}