#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include<cstring>
#include<deque>
#define itn int
#define coder goodboy
using namespace std;
typedef long long LL;typedef unsigned long long ULL;
const int maxn=30,maxv=30010;
int n,w[maxn],v[maxn],f[maxv],c[maxn],temp,maxmoney,ans=-1;
inline void in(){
	freopen("happy.in","r",stdin);
	freopen("happy.out","w",stdout);
	scanf("%d%d",&maxmoney,&n);
	for (int i=1;i<=n;i++){
		scanf("%d%d",&c[i],&temp);
		w[i]=c[i]*temp;
	}
}
inline void dp(){
	memset(f,0,sizeof(f));
	for (int i=1;i<=n;i++){
		for (int v=maxmoney;v>=c[i];v--){
			f[v]=max(f[v],f[v-c[i]]+w[i]);
			ans=max(ans,f[v]);
		}
	}
}
inline void p(){
	printf("%d",ans);
}
int Main(){
	in();
	dp();
	p();
	return 0;
}
int main(){;}
int goodboy=Main();