let string s period k s_i s_i k 1 s k s mean length string s k minimum positive integer propertySome example period s0101 period k2 s0000 period k1 s010 period k2 s0011 period k4you give string t consist 0s 1s need find string s String s consist 0s 1s the length s do not exceed 2 cdot t string t subsequence stre s String s small possible period string meet condition 13 let recall t subsequence s t derive s delete zero element change order remain element for example t011 subsequence s10101