View Code of Problem 18

#include<stdio.h>
int main(){
	int arr[1000] = {0};
	arr[3] = 1;
	arr[4] = 2;
	int x = 2, i;
	for(i = 5; i < 1000; i ++){
		arr[i] = arr[i - 1] + x;
		x ++;
	}
	int n;
	while(~scanf("%d", &n)){
		printf("%d\n", arr[n]);
	}
	return 0;
}

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