You are using both iostream and cstdio to handle input and output, remove line with ios::sync_with_stdio(0); and everything should be ok (I tried this on ideone.com and it wrote 0.250).

By the way you shouldn't call a function inside Abs, because for example Abs(solve(n+1,f+1) + ar[n]) will be translated to ((solve(n+1,f+1) + ar[n]) > 0? solve(n+1,f+1) + ar[n] : -(solve(n+1,f+1) + ar[n])) so function solve will be called twice, just saying, sometimes it can increase complexity a lot.