#include <iostream>
#include <stdio.h>
#include <string.h>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <math.h>
#include <bitset>
#include <algorithm>
#include <climits>
using namespace std;
#define LL long long
#define N 51000
#define mod 1000000007
#define INF 0x3f3f3f3f
#define lson root<<1
#define rson root<<1|1
int dp[N];
int w[N],v[N];
int main()
{
    freopen("happy.in","r",stdin);
    freopen("happy.out","w",stdout);
    int n,m;
    while(scanf("%d %d",&n,&m)!=EOF)
    {
        for(int i=1;i<=m;i++)
        {
            scanf("%d %d",&w[i],&v[i]);
            v[i] = w[i]*v[i];
        }
        memset(dp,0,sizeof(dp));
        for(int i=1;i<=m;i++)
        {
            for(int j=n;j>=w[i];j--)
                dp[j] =max(dp[j],dp[j-w[i]]+v[i]);
        }
        printf("%d\n",dp[n]);
    }
    return 0;
}