"use strict"
function main(arg) {
    var text = arg.trim().split("\n").map(Number).sort()
    for (var i = 1; i <= 3; i++) {
        if (!includeValue(i, text)) {
            console.log(i)
            break
        }
    }
}

function includeValue(x, arr) {
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] === x) {
            return true
        }
    }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));