I know the Schengen rule refers to 90 days in 180 days but how do you calculate it if, on part of your tour, you visit a non Schengen country. For instance you leave the UK at beginning of January and spend 2 months in France and Italy before moving into Croatia. You spend 2 months here. Then you travel back into France and stay another month. In theory I have spent 3 months in a Schengen country and 2 months in a non Schengen, making 5 months in total, would this be allowed and if so how would the authorities police it