View Compilation Error

0_0_18595971_19929.cpp: In function 'int main()':
0_0_18595971_19929.cpp:7:23: error: 'sqrt' was not declared in this scope
     i=ceil(sqrt(s[k-1])),puts(s[k]<=n&&i*i<n&&(s[k]+1!=n||n-i*i!=k)?"YES":"NO");
                       ^
0_0_18595971_19929.cpp:7:24: error: 'ceil' was not declared in this scope
     i=ceil(sqrt(s[k-1])),puts(s[k]<=n&&i*i<n&&(s[k]+1!=n||n-i*i!=k)?"YES":"NO");
                        ^