{"problem":{"name":"Energy Drink Collector","description":{"content":"Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up $M$ cans of energy drinks. There are $N$ stores that sell energy drinks. In the $i$\\-th store, he can buy at most","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"abc121_c"},"statements":[{"statement_type":"Markdown","content":"Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up $M$ cans of energy drinks.\nThere are $N$ stores that sell energy drinks. In the $i$\\-th store, he can buy at most $B_i$ cans of energy drinks for $A_i$ yen (the currency of Japan) each.\nWhat is the minimum amount of money with which he can buy $M$ cans of energy drinks?\nIt is guaranteed that, in the given inputs, a sufficient amount of money can always buy $M$ cans of energy drinks.\n\n## Constraints\n\n*   All values in input are integers.\n*   $1 \\leq N, M \\leq 10^5$\n*   $1 \\leq A_i \\leq 10^9$\n*   $1 \\leq B_i \\leq 10^5$\n*   $B_1 + ... + B_N \\geq M$\n\n## Input\n\nInput is given from Standard Input in the following format:\n\n$N$ $M$\n$A_1$ $B_1$\n$A_2$ $B_2$\n$\\vdots$\n$A_N$ $B_N$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"abc121_c","tags":[],"sample_group":[["2 5\n4 9\n2 4","12\n\nWith $12$ yen, we can buy one drink at the first store and four drinks at the second store, for the total of five drinks. However, we cannot buy $5$ drinks with $11$ yen or less."],["4 30\n6 18\n2 5\n3 10\n7 9","130"],["1 100000\n1000000000 100000","100000000000000\n\nThe output may not fit into a $32$\\-bit integer type."]],"created_at":"2026-03-03 11:01:14"}}