先判断休息时间加上歌唱时间是否超过活动时间，再尽量增多笑话的个数。
#include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#define MAX 100005
#define mod 998244353ll
#define INF 0x3f3f3f3f
#define ll long long
using namespace std;
int main() {
freopen(
"a.txt",
"r", stdin);
freopen(
"b.txt",
"w", stdout);
int n, d, a[
105];
cin >> n >> d;
int s =
0;
for (
int i =
1; i <= n; ++i) {
scanf(
"%d", &a[i]);
s += a[i];
}
s += (n -
1) *
10;
if (s <= d) {
cout << (n -
1) *
2 + (d - s) /
5 << endl;
}
else {
cout << -
1 << endl;
}
return 0;
}
