/*
	?§£????????????:Area of Polygon
	(http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0079)

	-status:

	-comment
        aaa
*/
var log = console.log;
if (typeof process != "undefined") {
    var input = "";
    process.stdin.resume();
    process.stdin.setEncoding('utf8');
    process.stdin.on('data', function(chunk) {
        input += chunk;
    });
    process.stdin.on('end', function() {
        var lines = input.split("\n");
        main(lines);
    });
}


function main(lines) {
    lines = lines.map(function(line) {
        return line.split(",").filter(function(e) {
            return e != "";
        }).map(function(e) {
            var n = Number(e);
            if (n.toString() == "NaN") {
                return e.replace(/(\r)|(\n)/g, "");
            }
            return n;
        });
    });
    var points = lines;
    var length = points.length;
    var p0 = points[0];
    var ps, pe;
    var S = 0;
    for (var i = 1; i < length - 1; i++) {
        //i = 1,2,3,,,,length-2
        ps = points[i];
        pe = points[i + 1];
        S += s(p0, ps, pe);
    }
    log(S);
}

function s(p1, p2, p3) {
    var a = dist(p1, p2);
    var b = dist(p2, p3);
    var c = dist(p3, p1);
    var z = (a + b + c) / 2;
    var z_a = z - a;
    var z_b = z - b;
    var z_c = z - c;
    return Math.sqrt(z * z_a * z_b * z_c);
}

function dist(p1, p2) {
    return Math.sqrt(
        Math.pow(p1[0] - p2[0], 2) +
        Math.pow(p1[1] - p2[1], 2)
    );
}