new file: B3984.cpp

B3984.cpp

@@ -0,0 +1,7 @@
+#include<bits/stdc++.h>
+using namespace std;
+long long x, y;
+int main() {
+    scanf("%lld%lld", &x, &y);
+    printf("%lld\n", (long long) ceil((y - x) / (long double)2.0));
+}