#include<bits/stdc++.h>
using namespace std;
int n, m, v[30], p[30], dp[30005];
int main(){
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= m; i++) scanf("%d%d", &v[i], &p[i]);
    for(int i = 1; i <= m; i++)
        for(int j = n; j >= v[i]; j--)
        dp[j] = max(dp[j], dp[j- v[i]] + v[i] * p[i]);
    printf("%d", dp[n]);
    return 0;    
}