提出 #71471976

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ソースコード 拡げる

#include <bits/stdc++.h>
#define int long long
using namespace std;
namespace IO {
	template<typename T> inline void read(T &x) {
		bool f = 1;
		x = 0;
		char ch = getchar();
		while (ch < '0' || ch > '9') {
			if (ch == '-')f = 0;
			ch = getchar();
		}
		while (ch >= '0' && ch <= '9') x = (x << 1) + (x << 3) + (ch & 15), ch = getchar();
		x = f ? x : -x;
	}
	template<typename T> inline void write(T x) {
		if (x < 0) putchar('-'), x = -x;
		if (x > 9) write(x / 10);
		putchar(('0' + x % 10));
	}
	template <typename T, typename ...Args> inline
	void read(T &x, Args &...args) {read(x),read(args...);}
	template<typename T> inline void write(T x, char c) {write(x), putchar(c);}
}
using namespace IO;
const int INF=1e18;

int n;

signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);

	cin>>n;
	cout<<(1+n)*n/2<<"\n";

	return 0;
}

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