give encode string return decode stringThe encoding rule kencoded_stre encoded_stre inside square bracket repeat exactly k time note k guarantee positive integeryou assume input string valid extra white space square bracket wellforme etc furthermore assume original datum contain digit digit repeat number k for example input like 3a 24the test case generate length output exceed 105 Example 1input s 3a2bcoutput aaabcbcExample 2input s 3a2coutput accaccaccExample 3input s 2abc3cdefoutput abcabccdcdcdef Constraints1 slength 30s consist lowercase english letter digit square brackets s guarantee valid inputall integer s range 1 300