The ornamental design for a stringedinstrument, as shown and described.
FIG. 1 is a left-front perspective view of a stringed instrument showing our new design.
FIG. 2 is a right-rear perspective view thereof.
FIG. 3 is a front elevation view thereof.
FIG. 4 is a rear elevation view thereof.
FIG. 5 is a left side elevation view thereof.
FIG. 6 is a right side elevation view thereof.
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a top plan view thereof.
Broken lines in the attached drawings are included for the purpose of illustrating portions of the stringed instrument and form no part of the claimed design.