let n = + gets();

let arr = new Array(n+1);

arr.fill(true);

arr[0] = false;
arr[1] = false;

for (let i = 2; i <= Math.round(Math.sqrt(n)); i++) {

    if (arr[i]) {
        let count = 0;

        for (let j = Math.pow(i, 2); j <= n;) {
            arr[j] = false;
            count++;
            j = Math.pow(i, 2) + count * i;
        }

    }

}

for (let i = arr.length; i >= 0; i--) {
    if (arr[i]) {
        print(i);
        break;
    }

}