#include<bits/stdc++.h>
using namespace std;
const int N = 1e4+114;
int f[N][N],val[N],w[N];
int n,m,sum;
int main(){
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		int x,y;
		cin>>x>>y;
		w[i] = x;
		val[i] = x*y;
	}
	for(int i=1;i<=m;i++){
		for(int j=0;j<=n;j++){
			f[i][j] = f[i-1][j];
			if(j>=w[i]){
				f[i][j] = max(f[i][j],f[i-1][j-w[i]]+val[i]);
			}
		}
	}
	sum = INT_MIN;
	for(int i=1;i<=m;i++){
		for(int j=0;j<=n;j++){
			sum = max(sum,f[i][j]);
		}

	}
	cout<<sum;
	return 0;
}