function arrInt(arr) {
    return arr.map(str => parseInt(str, 10))
        .sort((a, b) => a - b);
}
function Main(input) {
    const src = input.split("\n");
    const n = parseInt(src[0]);
    const a = arrInt(src[1].split(" "));
    let ans = a[0];
    for (let i = 1; i < n; i++) {
        if (a[i - 1] != (a[i] - 1)) ans += a[i];
    }
    console.log(ans);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));