const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void (async function () {
    // Write your code here
    while ((line = await readline())) {
        const num = +line;
        const a = 6;
        const b = 8;
        for (let i = Number.parseInt(num / 8); i >= 0; i--) {
            const j = (num - i * b) / a;
            if (Number.isInteger(j)) {
                console.log(i + j);
                return;
            }
        }
        console.log(-1)
    }
})();