//THIS IS WORKING CODE
Microsoft.Office.Interop.Excel.Range Range_Number,r2;
Range_Number = wsheet.UsedRange.Find("smth");
string f_number="";
r2 = wsheet.Cells;
int n_c = Range_Number.Column;
int n_r = Range_Number.Row;
var number = ((Range)r2[n_r + 1, n_c]).Value;
f_number = (string)number;