const input = require('fs').readFileSync('/dev/stdin', 'utf8');
const [B] = input.split('\n').map(v => v.split(/\s/).map(v => Number(v)));
const ans = [...Array(10).keys()].map(v => v + 1);
for (i in B) {
  if (B[i] != ans[i]) {
    console.log(ans[i]);
    break;
  } else if (i == 8) {
    console.log(10);
  }
}