const lines = require('fs')
  .readFileSync('/dev/stdin', 'utf-8')
  .trim().split('\n').values();

const A = Number(lines.next().value);

let ans = -1;

for (let i = 2; i <= A; i++) {
  if (Math.floor(A / i) === 1 && A % i === 7) {
    ans = i;
    break;
  }
}

console.log(ans);