Is there a single food that you can live on without any problems? Unfortunately the answer is no. There is no single food (other than breast milk for infants) that can sustain all of our nutritional needs.
However, the potato actually comes closest to being a perfect food! Potatoes have an unusual amount of protein and wide variety of nutrients. However if potatoes were the only thing eaten, a human would still have nutritional deficiencies.
Potatoes have protein, potassium, vitamin B6, magnesium, and actually have 70% of the amount of Vitamin C you need per day!
Recently, an Australian man ate only potatoes for one year. He included sweet potatoes to get more vitamins A and E, iron, and calcium. He did reasonably well for one year and lost weight. However researchers note that this diet would not prove enough B vitamins and zinc.