开 longlong！
求关
by louliu @ 2024-03-28 20:53:00
@[WCX12312](/user/1253413) ，最坏情况答案在 $10^6 \times 10^6$ 级，要开 `long long`
by Lucky_Cloud @ 2024-03-28 20:53:01
```cpp
#include <bits/stdc++.h>
using namespace std;
long long a[1000005];
int main(){
long long a1,a2,n,x,sum=0;
cin>>a1>>a2>>n;
x=a2-a1;
a[1]=a1;
a[2]=a2;
for(int i=3;i<=n;i++){
a[i]=a[i-1]+x;
}
for(int i=1;i<=n;i++){
sum+=a[i];
}
cout<<sum;
return 0;
}
```
by louliu @ 2024-03-28 20:53:31