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#include<bits/stdc++.h>
using namespace std;
int dp[100005];
int main(){
int n , m;
cin >> n >> m;
int w[100005] , j[100005];
for(int i = 1;i <= m;i++) cin >> w[i] >> j[i];
for(int i = 1;i <= n;i++){
for(int k = n;k >= w[i];k--)
dp[k] = max(dp[k],dp[k-w[i]] + w[i] * j[i]);
}
cout << dp[n];
return 0;
}