素数个数

{
  "problem": {
    "name": "素数个数",
    "description": {
      "content": "编程求 $2\\sim n$（$n$ 为大于等于 $2$ 的正整数）中有多少个素数。",
      "description_type": "Markdown"
    },
    "platform": "Luogu",
    "limit": {
      "time_limit": 1000,
      "memory_limit": 131072
    },
    "difficulty": {
      "LuoguStyle": "P1"
    },
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "LGB2128"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "编程求 $2\\sim n$（$n$ 为大于等于 $2$ 的正整数）中有多少个素数。\n\n## Input\n\n输入 $n(2 \\le n \\le 50000)$。\n\n## Output\n\n输出一行，表示 $2\\sim n$ 中的素数个数。\n\n[samples]\n\n## Note\n\n对于所有数据，保证 $2 \\le n \\le 50000$。...",
      "is_translate": false,
      "language": "English"
    }
  ]
}