.js

var cities = 0;
var roads = 0;
var line = readline().split(" ").map((e) => {
    return parseInt(e)
});
cities = line[0];
roads = line[1];
while (cities > 0) {
    if (roads > 0) {
        var group = [];
        for (var i = 0; i < cities; i++) {
            group.push([i + 1])
        }
        for (var i = 0; i < roads; i++) {
            road = readline().split(" ").map((e) => {
                return parseInt(e)
            });
            var groupa, groupb;
            for (var j = 0; j < group.length; j++) {
                if (group[j].indexOf(road[0]) > -1) {
                    groupa = j;
                    break;
                }
            }
            for (var j = 0; j < group.length; j++) {
                if (group[j].indexOf(road[1]) > -1) {
                    groupb = j;
                    break;
                }
            }
            if (groupa != groupb) {
                group[groupa] = group[groupa].concat(group[groupb]);
                group.splice(groupb, 1);
            }
        }
        print(group.length - 1);
    } else {
        print(cities - 1);
    }

    line = readline().split(" ").map((e) => {
        return parseInt(e)
    });
    cities = line[0];
    roads = line[1];
}