could not copy obj debug exe to bin debug exe Visual studio 2015 error fixing

Unable to copy file "obj\Debug\app1.exe" to "bin\Debug\app1.exe". The process cannot access the file 'bin\Debug\app1.exe' because it is being used by another process. app1 Error 2 Could not copy "obj\Debug\app1.exe" to "bin\Debug\app1.exe". Exceeded retry count of 10. Failed. app1 fixing of these two errors