//bridge
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define fo(i,j,k) for(i=j;i<=k;i++)
using namespace std;
int n,W,ans=1e9;
int yu[20],mx[20];
bool b[20];
struct person {int w,t;} p[20];
inline bool comp(const person &x,const person &y)
{
return x.t>y.t;
}
inline void dfs(int num,int now)
{
int i,j;
if(now>=ans) return;
if(num>n)
{
ans=now;
return;
}
fo(i,1,num)
if(p[num].w<=yu[i])
{
yu[i]-=p[num].w;
int tmp=mx[i];
if(p[num].t>mx[i])
mx[i]=p[num].t,dfs(num+1,now+p[num].t-tmp);
else
dfs(num+1,now);
mx[i]=tmp;
yu[i]+=p[num].w;
}
}
int main()
{
int i,j,k;
scanf("%d%d",&W,&n);
fo(i,1,n)
scanf("%d%d",&p[i].t,&p[i].w),yu[i]=W;
sort(p+1,p+n+1,comp);
dfs(1,0);
printf("%d\n",ans);
return 0;
}
/*
100 3
24 60
10 40
18 50
*/
