{"problem":{"name":"Sum of product of pairs","description":{"content":"Given are $N$ integers $A_1,\\ldots,A_N$. Find the sum of $A_i \\times A_j$ over all pairs $(i,j)$ such that $1\\leq i < j \\leq N$, modulo $(10^9+7)$.","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"abc177_c"},"statements":[{"statement_type":"Markdown","content":"Given are $N$ integers $A_1,\\ldots,A_N$.\nFind the sum of $A_i \\times A_j$ over all pairs $(i,j)$ such that $1\\leq i < j \\leq N$, modulo $(10^9+7)$.\n\n## Constraints\n\n*   $2 \\leq N \\leq 2\\times 10^5$\n*   $0 \\leq A_i \\leq 10^9$\n*   All values in input are integers.\n\n## Input\n\nInput is given from Standard Input in the following format:\n\n$N$\n$A_1$ $\\ldots$ $A_N$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"abc177_c","tags":[],"sample_group":[["3\n1 2 3","11\n\nWe have $1 \\times 2 + 1 \\times 3 + 2 \\times 3 = 11$."],["4\n141421356 17320508 22360679 244949","437235829"]],"created_at":"2026-03-03 11:01:14"}}