function Main(ldata){
	let data = ldata.trim().split(/\n|\r\n/)[1];
	let i = 0;
	
	while(data.match("000") != null){
		data.replace("000","010");
		i++;
	}
	
	i += data.match("00").length;
	console.log(i);
}

Main(require('fs').readFileSync('/dev/stdin','utf8'));