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本题很简单主要考察的是对int long类型的限制问题

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算法

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        int n = new Scanner(System.in).nextInt();

        System.out.println((long)n*(n+1)/2);

    }

}

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int 长度限制是10位

long 长度限制是19位