View Compilation Error

0_0_28856973_7811.cpp:2:1: error: 'usina' does not name a type
 usina namespace std;
 ^
0_0_28856973_7811.cpp: In function 'void Floyd()':
0_0_28856973_7811.cpp:11:46: error: 'max' was not declared in this scope
     a[i][j] = max( a[i][j] , a[i][k]*a[k][j] );
                                              ^
0_0_28856973_7811.cpp:11:46: note: suggested alternative:
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/algorithm:62:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/x86_64-w64-mingw32/bits/stdc++.h:64,
                 from 0_0_28856973_7811.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_algo.h:3454:5: note:   'std::max'
     max(initializer_list<_Tp> __l, _Compare __comp)
     ^