$CODE:$

#include<bits/stdc++.h>
#define int long long
using namespace std;
struct node{
    int d;
    int y;
    double c;
    bool operator<(const node&x)const{
        return c<x.c;
    }
};
signed main(){
    int n,m;
    cin>>n>>m;
    vector<node>ca(m);
    for(int i=0;i<m;i++) {
        cin>>ca[i].y;
        ca[i].d=i+1;
        ca[i].c=(double)ca[i].y/ca[i].d;
    }
    sort(ca.begin(),ca.end());
    int ta=0;
    int t=0;
    for(auto&z:ca) {
        if(ta+z.d<=n){
            ta+=z.d;
            t+=z.y;
        }else{
            int r=n-ta;
            t+=r*z.c;
            break;
        }
    }
    cout<<t<<endl;
    return 0;
}

$此代码只有 18pts$