ABC 048, finished all with help of editorial

atcoder/beginner_contests/abc048/src/bin/b.rs

@@ -0,0 +1,21 @@
+use proconio::input;
+
+fn f(n: i64, x: i64) -> i64 {
+    if n == -1 {
+        0
+    } else {
+        n / x + 1
+    }
+}
+
+fn main(){
+    input!{
+        a: i64,
+        b: i64,
+        x: i64,
+    };
+
+    let result = f(b, x) - f(a - 1, x);
+
+    println!("{}", result);
+}