#include <iostream>
using namespace std;
const int N = 30010;
int f[N];
int main() {
int n, m;
scanf("%d%d", &n, &m);
for (int i = 1; i <= m; i ++) {
int v, p;
scanf("%d%d", &v, &p);
for (int j = n; j >= v; j --) {
f[j] = max(f[j], f[j - v] + v * p);
}
}
printf("%d", f[n]);
return 0;
}