fun main(args: Array<String>) = with(System.`in`.bufferedReader()){
var (r,c,w) = readLine().split(" ").map{it.toInt()}
var map = Array(r+w-1){
IntArray(it+1){1}
}
for(i in 2 until map.size){
for(j in 1 until map[i].size-1){
map[i][j] = map[i-1][j-1] + map[i-1][j]
}
}
var ans =0
for(i in r-1..r-1+w-1){
repeat(i-r+2){
ans +=map[i][it+c-1]
}
}
println(ans)
}