let readline  = require("readline");
const fs = require('fs');
let rl = readline.createInterface(process.stdin,process.stdout);
let r_str = '';
rl.on('line',function(m_str) {
  //console.log();
  rl.on('line',function(p_str) {
     let ans;
      if (m_str.length != p_str.length) {
         console.log(-1);
  }
  else{
   ans = kmp11(m_str,p_str);
       console.log(ans);

  }
       rl.close();
    process.exit();
  });

});



function kmp11(main_str_js,pattern_js) {
  let mas_prefix =new Array(pattern_js.length).fill(0);
  let result = [];
  let count = 0;
  let flag = 0;
  mas_prefix[0] = 0;
  for (let i = 1; i < pattern_js.length; ++i) {
    count = mas_prefix[i-1];
    while ((count > 0) && (pattern_js[i] != pattern_js[count])){
      count = mas_prefix[count-1];
    }
    if (pattern_js[i] == pattern_js[count]){
      count++;
    }
    mas_prefix[i] = count;
  }
  count = 0;
  for (let i = 0; i < main_str_js.length; ++i)
  {
  while ((count > 0) && (pattern_js[count] != main_str_js[i])){
      count = mas_prefix[count-1];
  }
  if (pattern_js[count] == main_str_js[i]){
    count++;
  }
  //console.log(count);
}
  let ans = (main_str_js.length - count) ;
  //console.log(ans);
  //ans = result[1];
      if (count == main_str_js.length){
        ans = 0;
        count = 0;
      }
  else{
  for (let i = 0; i < main_str_js.length - count; i++) {
    if (pattern_js[i+count] != main_str_js[i])
      ans = -1;
  }
  }

return ans;
};