abc319_d
$显然L不能设置成0$
$L满足L >= max(len_1,len_2…len_n)$
$R满足R <= sum(len_1 + 1,len_2 + 1…len_n + 1)$

int a[200005];
int n, m;
int check(int x){
    int res = x;
    int cnt = 1;
    for(int i = 1; i <= n; ++ i){
        if(res == x){
            res -= a[i];
        }
        else{
            if(res < a[i] + 1){
                res = x;
                ++ cnt;
            }
            if(res == x){
                res -= a[i];
            }
            else res -= a[i] + 1;
        }
    }
    return cnt <= m;
}
void solve(){
    n = read(), m = read();
    int l = 0, r = 0;
    for(int i = 1; i <= n; ++ i){
        a[i] = read();
        l = max(l, a[i]);
        r += a[i] + 1;
    }
    while(l < r){
        int mid = l + r >> 1;
        if(check(mid)) r = mid;
        else l = mid + 1;
    }
    cout << l;

}