function main(input) {
  let [N] = getIntegers(input, " ");
  let [K] = getIntegers(input, " ");
  let prime = primeList(N, K);
  let hash = hashList(prime);
  let idx = solve(hash);
  console.log(prime[idx]);
}

function solve(L) {
  let i=0, j=0, max=0, maxI=0;
  let LL = [];
  while(j < L.length) {
    let idx = LL.indexOf(L[j], i);
    if(idx >= 0) i=idx+1;
    LL.push(L[j]);
    j++;
    if(max <= j-i) {
      max = j-i;
      maxI = i;
    }
  }
  return maxI;
}

function hashList(L) {
  let list = [];
  for(let i=0; i<L.length; i++) {
    let LS = L[i].split("");
    while(true) {
      if(LS.length > 1) {
        sum = 0;
        for(let j=0; j<LS.length; j++) {
          sum += Number(LS[j]);
        }
        LS = String(sum).split("");
      } else {
        list.push(LS[0]);
        break;
      }
    }
  }
  return list;
}

function primeList(N, K) {
  let list = new Array(K+1).fill(true);
  list[0] = false;
  list[1] = false;
  for(let i=2; i<=Math.sqrt(K); i++) {
    if(list[i] == true) {
      for(let j=i*2; j<=K; j+=i) {
        list[j] = false;
      }
    }
  }
  let out = [];
  for(let i=2; i<list.length; i++) {
    if(list[i] && i >= N) out.push(String(i));
  }
  return out;
}

//-- functions ---------------------------------------------------------------
function getIntegers(l, s) {return s === undefined ? l.map(x=>Number(x)) : l.shift().split(s).map(x=>Number(x))}

main(require("fs").readFileSync("/dev/stdin", "utf8").trim().split("\n"));