#include <stdio.h>

int main() {

  int r,d,n,i,j,k,l;
  int p,c;
  int a[60] = {0};
  int b[60] = {0};


  while(1) {

    scanf("%d %d", &n, &r);

    if(n == 0 && r == 0) {
      break;
    }


    for(i =0 ; i<=n ; i++) {
      a[n-1-i] = i+1;
      b[n-1-i] = i+1;
    }



    for(i = 0; i < r; i++) {
      scanf("%d %d",&p,&c);

      for(j = 0; j<c;j++) {
	a[j] = b[p+j-1];
	//printf("a[%d] = %d\n",j,a[j]);
      }
      for(j = 0;j<p-1;j++) {
	a[c+j] = b[j];
	//printf("a[%d] = %d\n" ,c+j ,a[c+j]);
      }

      for(j = 0;j<p+c-1;j++) {
	b[j] = a[j];
      }
    }


    printf("%d\n",a[0]);

  }

  return 0;
}