https://codeforces.com/contest/1141/problem/E 

题解： 

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=200000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const ll INF = 0x3f3f3f3f3f3f3f3f;
int t,n,m,k,q;
unsigned long long  ans;
ll cnt,flag,temp,sum;
ll h;
int a[N];
char str;
struct node{};
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    //scanf("%d",&t);
    //while(t--){
    scanf("%I64d%d",&h,&n);
    ll H=h;
    ll minl=INF;
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        sum+=a[i];
        minl=min(minl,sum);
        if(h+sum<=0){
            cout<<i<<endl;
            return 0;
        }
    }
    if(minl>=0||sum>=0){
        cout<<-1<<endl;
        return 0;
    }
    cnt=(H+minl)/-sum;
    if((H+minl)%-sum)
        cnt++;
    ans=(unsigned long long)cnt*n;
    h=H+sum*cnt;
    if(h<=0){
        cout<<ans<<endl;
        return 0;
    }
    for(int i=1;i<=n;i++){
        h+=a[i];
        if(h<=0){
            cout<<ans+i<<endl;
            return 0;
        }
    }

    //}

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}