CodeForces 546A A Contest #1(A. Soldier and Bananas)

Asoldierwantstobuywbananasintheshop.Hehastopaykdollarsforthefirstbanana,2kdollarsforthesecondoneandsoon(inotherwords,hehastopayi·kdollarsforthei-thbanana).Hehasndollars.Howmanydollarsdoeshehavetoborrowfromhisfriendsoldiertobuywbananas?InputThefirstlinecontainsthreepositiveintegersk, n, w(1  ≤  k, w  ≤  1000,0 ≤ n ≤ 109),thecostofthefirstbanana,initialnumberofdollarsthesoldierhasandnumberofbananashewants.OutputOutputoneinteger—theamountofdollarsthatthesoldiermustborrowfromhisfriend.Ifhedoesn'thavetoborrowmoney,output0.SampleInputInput3174Output13这个题目是意思是有ndollar，thefirstbananacostkdollars，第i个就需costk*i，问买w个bananas是否需要借钱；借钱需要多少？分析：首先计算w个bananas需要多少money，在与n比较。#include<iostream>#include<cstdio>usingnamespacestd;intmain(){intk,n,w,b;inti;while(scanf("%d%d%d",&k,&n,&w)==3){intsum=0;for(i=1;i<=w;i++)sum+=i*k;//计算w个bananas所需的money

　b=sum-n;//比较总需费与n的大小，最后输出b的结果
if(b==0||b<0)
printf("0\n");
else
printf("%d\n",b);

}return0;}