#include<bits/stdc++.h>
#define LL long long
#define MAXSIZE 1005
#define INF 0x3f3f3f3f

using namespace std;

struct node
{
    int val;
    int pic;
}p[30];

int dp[30005];

int main()
{
    freopen("happy.in","r","stdin");
    freopen("happy.out","w","stdout");
    int n,m,ans=0;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&p[i].pic,&p[i].val);
    }
    memset(dp,0,sizeof(dp));
    for(int i=1;i<=m;i++)
    {
        for(int j=n;j>=p[i].pic;j--)
        {
            dp[j] = max(dp[j],dp[j-p[i].pic] + p[i].pic*p[i].val);
            ans = max(ans,dp[j]);
        }
    }
    printf("%d\n",ans);
    return 0;
}