Android Question firebase problem when open app and crashed

hello, i have this problem in my app when try to open:

Logger connesso a: OPPO CPH2197
--------- beginning of main
*** Service (starter) Create ***
** Service (starter) Start **
** Activity (main) Create (first time) **
main_activity_create (java line: 1895)
java.lang.NoClassDefFoundError: Failed resolution of: Lcom/google/android/gms/ads/InterstitialAd;
at mobi.mindware.admob.interstitial.AdmobInterstitialsAds.Initialize(AdmobInterstitialsAds.java:48)
at com.partannasoftware.scherzo.main._activity_create(main.java:1895)
at java.lang.reflect.Method.invoke(Native Method)
at anywheresoftware.b4a.BA.raiseEvent2(BA.java:221)
at com.partannasoftware.scherzo.main.afterFirstLayout(main.java:105)
at com.partannasoftware.scherzo.main.access$000(main.java:17)
at com.partannasoftware.scherzo.main$WaitForLayout.run(main.java:83)
at android.os.Handler.handleCallback(Handler.java:942)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:240)
at android.os.Looper.loop(Looper.java:351)
at android.app.ActivityThread.main(ActivityThread.java:8355)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:584)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1013)
Caused by: java.lang.ClassNotFoundException: com.google.android.gms.ads.InterstitialAd
... 15 more
main_activity_create (java line: 1895)
java.lang.NoClassDefFoundError: Failed resolution of: Lcom/google/android/gms/ads/InterstitialAd;
at mobi.mindware.admob.interstitial.AdmobInterstitialsAds.Initialize(AdmobInterstitialsAds.java:48)
at com.partannasoftware.scherzo.main._activity_create(main.java:1895)
at java.lang.reflect.Method.invoke(Native Method)
at anywheresoftware.b4a.BA.raiseEvent2(BA.java:221)
at com.partannasoftware.scherzo.main.afterFirstLayout(main.java:105)
at com.partannasoftware.scherzo.main.access$000(main.java:17)
at com.partannasoftware.scherzo.main$WaitForLayout.run(main.java:83)
at android.os.Handler.handleCallback(Handler.java:942)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:240)
at android.os.Looper.loop(Looper.java:351)
at android.app.ActivityThread.main(ActivityThread.java:8355)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:584)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1013)
Caused by: java.lang.ClassNotFoundException: com.google.android.gms.ads.InterstitialAd
... 15 more
helpme please, thanks