setw setfill

こどふぉ５４４div.3 A

# include<iostream>
# include<vector>
# include<algorithm>
# include<string>
# include<map>
# include<math.h>
# include<queue>
# include<deque>
# include<stack>
# include<cstdio>
# include<utility>
# include<set>
# include<list>
# include<cmath>
# include<stdio.h>
# include<string.h>
# include<iomanip>
using namespace std;
# define FOR(i, a, b) for (ll i = (a); i <= (b); i++)
# define REP(i, n) FOR(i, 0, n - 1)
# define NREP(i, n) FOR(i, 1, n)
using ll = long long;
using pii = pair<int, int>;
using piii = pair<pii, pii>;
const int dx[4] = { 0, -1, 1, 0 };
const int dy[4] = { -1, 0, 0, 1 };
const int INF = 1e9 + 7;
int gcd(int x, int y) {
	if (x < y)swap(x, y);
	if (y == 0)return x;
	return gcd(y, x%y);
}

template<class T1, class T2> void chmin(T1 &a, T2 b) { if (a>b)a = b; }

template<class T1, class T2> void chmax(T1 &a, T2 b) { if (a<b)a = b; }
template<class T>
void Add(T &a, const T &b, const T &mod = 1000000007) {
	int val = ((a % mod) + (b % mod)) % mod;
	if (val < 0) { val += mod; }
	a = val;
}
////////////////////////////////////////

int main() {
	int h1, h2, m1, m2;
	char char1, char2;
	cin >> h1 >> char1 >> m1;
	cin >> h2 >> char2 >> m2;
	int tmp = (h1 * 60 + h2 * 60 + m1 + m2) / 2;
	int ans1 = tmp / 60;
	int ans2 = tmp % 60;
	cout << setw(2) << setfill('0')<< ans1;
	cout << ':';
	cout << setw(2) << setfill('0') << ans2 << endl;
	return 0;
}

setw,setfillとかいう新しい学びを得た