#include<bits/stdc++.h>
using namespace std;
const int maxn=30;
int n,m;
int v[maxn],p[maxn],w[maxn],f[30005];
int main()
{
	freopen("happy.in","r",stdin); 
	freopen("happy.out","w",stdout); 
    cin>>n>>m;
    for(int i=1,a,b;i<=m;i++)
    {
        scanf("%d%d",&a,&b);
        v[i]=a;
        p[i]=b;
        w[i]=v[i]*p[i];
    }
    for(int i=1;i<=m;i++)
    {
        for(int j=n;j>=v[i];j--)
        {
            f[j]=max(f[j],f[j-v[i]]+w[i]);
        }
    }
    cout<<f[n]<<endl;
    return 0;
}