!     F77 Version.  NCCS = 21

      SUBROUTINE echo_f77(N, niters, check)
      INTEGER N, niters, iter
      REAL check
      REAL P1(N,N), P2(N,N), P3(N,N), C(N,N)
      INTEGER i, j

      CALL echo_f77_setInitialConditions(c, P1, P2, P3, N)

      DO iter=1, niters
        DO j=2,N-1
          DO i=2,N-1
            P3(i,j) = (2-4*c(i,j))*P2(i,j) + c(i,j)*(P2(i,j-1) 
     .          + P2(i,j+1) + P2(i-1,j) + P2(i+1,j)) - P1(i,j)
          END DO
        END DO

        DO j=1,N
          DO i=1,N
            P1(i,j) = P2(i,j)
            P2(i,j) = P3(i,j)
          END DO
        END DO
      END DO

      check = P1(N/2,N/2)

      RETURN
      END