cf(#div1 A. Dreamoon and Sums)(数论)

A. Dreamoon and Sums

time limit per test
1.5 seconds

memory limit per test
256 megabytes

input
standard input

output
standard output

Dreamoon loves summing up something for no reason. One day he obtains two integers a and b occasionally. He wants to calculate the sum of all nice integers. Positive integer x is called nice if

#include<cstdio>
#include<cstring>
#define LL __int64
#define mod 1000000007
int main()
{
LL  a,b;
LL sum;
while(scanf("%I64d%I64d",&a,&b)!=EOF)
{
sum=0;
for(LL j=1;j<=a;j++)
{
sum+=((j*b)%mod+1)%mod;
sum%=mod;
}
LL ans=(((b-1)*b)/2)%mod;
printf("%I64d\n",(sum*ans)%mod);
}
return 0;
}

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