#include <iostream>
#include <algorithm>
using namespace std;

int main() {
    int N, m;
    cin >> N >> m;
    
    int v[25]; // 物品价格
    int w[25]; // 物品重要度
    int dp[30001] = {0}; // 动态规划数组，初始化为0
    
    for (int i = 0; i < m; i++) {
        cin >> v[i] >> w[i];
    }
    
    for (int i = 0; i < m; i++) {
        for (int j = N; j >= v[i]; j--) {
            dp[j] = max(dp[j], dp[j - v[i]] + v[i] * w[i]);
        }
    }
    
    cout << dp[N] << endl;
    
    return 0;
}