#include <stdio.h>
#include <stdlib.h>


struct claster
{
    int end;
};

struct Pqueue
{
    int cap,count;
    struct claster *h;
};

void InitPqueue(struct Pqueue* pq, int ClastCount)
{
    pq->h = (struct claster*)malloc(ClastCount * sizeof(struct claster));
    pq->cap = ClastCount;
    pq->count = 0;
}

void insert(struct Pqueue *pq,int ptr)
{
        int i;
        i=pq->count;
        pq->count=i+1;
	pq->h[i].end=ptr;
	struct claster Swap;
	while(i>0 && pq->h[(i-1)/2].end > pq->h[i].end)
	{
		Swap=pq->h[(i-1)/2];
		pq->h[(i-1)/2]=pq->h[i];
		pq->h[i]=Swap;
		i = (i-1)/2;
	}
}

void insert1(struct Pqueue *pq,int ptr)
{
        int i;
        i=pq->count-1;
	pq->h[i].end=ptr;
	struct claster Swap;
	while(i>0 && pq->h[(i-1)/2].end > pq->h[i].end)
	{
		Swap=pq->h[(i-1)/2];
		pq->h[(i-1)/2]=pq->h[i];
		pq->h[i]=Swap;
		i = (i-1)/2;
	}
}

void Heapify(struct Pqueue* pq)
{
        int l, r, j,i;
        struct claster swap;
   	for(i = 0;;)
	{
                l = 2*i+1;
                r = l+1;
                j = i;
                if(l < pq->count && pq->h[l].end < pq->h[j].end)
	        {
		        j = l;
	        }
                if(r < pq->count && pq->h[r].end < pq->h[j].end)
		{
			j = r;
		}
                if(i == j)
                {
                        break;
                }
                swap = pq->h[i];
                pq->h[i] = pq->h[j];
                pq->h[j] = swap;
                i = j;
        }
}

int main (int argc, char const *argv[])
{
	int ClastCount,i,NumOfOperations=0,swap=0;
	scanf("%d", &ClastCount );
        scanf("%d", &NumOfOperations );
	struct Pqueue pq;
	InitPqueue(&pq, ClastCount);
        int time[NumOfOperations][2];
	for(i = 0; i < ClastCount; i++)
	{
		scanf("%d", &time[i][0] );
                scanf("%d", &time[i][1] );
                time[i][1]+=time[i][0];
                insert(&pq,time[i][1]);
	}
        Heapify(&pq);
	for (; i<NumOfOperations; i++)
        {
                scanf("%d", &time[i][0] );
                scanf("%d", &time[i][1] );
                time[i][1]+=time[i][0];       
                if (pq.h[0].end < time[i][0])
                {
                        pq.h[0].end=time[i][1];
                }
                else
                {
                        pq.h[0].end+=time[i][1]-time[i][0];
                }
                swap=pq.h[0].end;
                pq.h[0].end=pq.h[pq.cap-1].end;
                insert1(&pq,swap);
                Heapify(&pq);
        }
        for (i=0;i<ClastCount;i++)
        {
                if (swap<pq.h[i].end)
                {
                        swap=pq.h[i].end;
                }
        }
        printf("%d",swap);
	free(pq.h);
	return 0;
}