{"raw_statement":[{"iden":"problem statement","content":"AtCoDeer has an empty piggy bank.  \nOn the morning of the $i$\\-th day, he will put $i$ yen (Japanese currency) in it: $1$ yen on the morning of the $1$\\-st day, $2$ yen on the morning of the $2$\\-nd day, and so on.  \nEach night, he will check the amount of money in it.  \nOn which day will he find out that his piggy bank has $N$ yen or more for the first time?"},{"iden":"constraints","content":"*   $1 \\le N \\le 10^9$\n*   $N$ is an integer."},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$N$"},{"iden":"sample input 1","content":"12"},{"iden":"sample output 1","content":"5\n\n*   On the $1$\\-st day, the piggy bank gets $1$ yen in the morning and has $1$ yen at night.\n*   On the $2$\\-st day, the piggy bank gets $2$ yen in the morning and has $3$ yen at night.\n*   On the $3$\\-rd day, the piggy bank gets $3$ yen in the morning and has $6$ yen at night.\n*   On the $4$\\-th day, the piggy bank gets $4$ yen in the morning and has $10$ yen at night.\n*   On the $5$\\-th day, the piggy bank gets $5$ yen in the morning and has $15$ yen at night.\n\nThus, on the $5$\\-th night, AtCoDeer will find out that his piggy bank has $12$ yen or more for the first time."},{"iden":"sample input 2","content":"100128"},{"iden":"sample output 2","content":"447"}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}