Alternatives to nested ifelse statements in R

Suppose we have the following data. The rows represent a country and the columns (in05:in09) indicate whether that country was present in a database of interest in the given year (2005:2009).

  id <- c("a", "b", "c", "d")
    in05 <- c(1, 0, 0, 1)
    in06 <- c(0, 0, 0, 1)
    in07 <- c(1, 1, 0, 1)
    in08 <- c(0, 1, 1, 1)
    in09 <- c(0, 0, 0, 1)
    df <- data.frame(id, in05, in06, in07, in08, in09)

I want to create a variable "firstyear" which indicates the first year in which the country was present in the database. Right now I do the following:

df$firstyear <- ifelse(df$in05==1,2005,
    ifelse(df$in06==1,2006,
        ifelse(df$in07==1, 2007,
            ifelse(df$in08==1, 2008,
                ifelse(df$in09==1, 2009,
                    0)))))

The above code is already not very nice, and my dataset contains many more years. Is there an alternative, using apply functions, loops or something else, to create this 'first year' variable?

Thanks again for your time and input.